diff --git a/aegisub/auto4_base.cpp b/aegisub/auto4_base.cpp
index 9674cea98..f802edc41 100644
--- a/aegisub/auto4_base.cpp
+++ b/aegisub/auto4_base.cpp
@@ -366,9 +366,7 @@ namespace Automation4 {
 
 		if (script_finished) {
 			if (!debug_visible) {
-				if(IsModal())
-					EndModal(0);
-				else Show(false);
+				EndModal(0);
 			} else {
 				cancel_button->Enable(true);
 				cancel_button->SetLabel(_("Close"));
@@ -452,10 +450,7 @@ namespace Automation4 {
 			cancelled = true;
 			cancel_button->Enable(false);
 		} else {
-			if(this->IsModal())
-				EndModal(0);
-			else
-				Show(false);
+			EndModal(0);
 		}
 	}
 
diff --git a/aegisub/auto4_base.h b/aegisub/auto4_base.h
index 963ca0ce9..f5dd180f0 100644
--- a/aegisub/auto4_base.h
+++ b/aegisub/auto4_base.h
@@ -232,6 +232,7 @@ namespace Automation4 {
 		void OnIdle(wxIdleEvent &evt);
 		void OnConfigDialog(ShowConfigDialogEvent &evt);
 
+		void DoUpdateDisplay();
 
 	protected:
 		volatile bool cancelled;
@@ -241,7 +242,6 @@ namespace Automation4 {
 		virtual ~ProgressSink();
 
 	public:
-		void DoUpdateDisplay();
 		void SetProgress(float _progress);
 		void SetTask(const wxString &_task);
 		void SetTitle(const wxString &_title);
diff --git a/aegisub/auto4_ruby.cpp b/aegisub/auto4_ruby.cpp
index 110e0691b..7fd0f31ff 100644
--- a/aegisub/auto4_ruby.cpp
+++ b/aegisub/auto4_ruby.cpp
@@ -56,7 +56,7 @@ namespace Automation4 {
 	RubyScript * RubyScript::inst = NULL; // current Ruby Script
 	RubyProgressSink* RubyProgressSink::inst = NULL;
 	VALUE RubyScript::RubyAegisub;
-	RubyAssFile *RubyAssFile::raf = NULL;
+//	RubyAssFile *RubyAssFile::raf = NULL;
 
 	// RubyScriptReader
 	RubyScriptReader::RubyScriptReader(const wxString &filename)
@@ -137,7 +137,8 @@ namespace Automation4 {
 			rb_protect(rbLoadWrapper, rb_str_new2(t), &status);
 			if(status > 0)	// something bad happened (probably parsing error)
 			{
-				//throw StringValueCStr(ruby_errinfo);
+				VALUE err = rb_errinfo();
+				throw StringValueCStr(err);
 			}
 
 			VALUE global_var = rb_gv_get("$script_name");
@@ -281,11 +282,20 @@ namespace Automation4 {
 			return true;
 
 		try {
+			RubyProgressSink::inst = NULL;
 			RubyAssFile *subsobj = new RubyAssFile(subs, true, true);
-			VALUE sel = CreateIntegerArray(selected); // selected items
-			RubyObjects::Get()->Register(sel);
-			VALUE result = rbFunCall(rb_mKernel, rb_to_id(validation_fun), 3, subsobj->rbAssFile, sel, rb_int2inum(active));
-			RubyObjects::Get()->Unregister(sel);
+			VALUE *argv = ALLOCA_N(VALUE, 3);
+			argv[0] = subsobj->rbAssFile;
+			argv[1] = CreateIntegerArray(selected); // selected items;
+			argv[2] = INT2FIX(active);
+			RubyCallArguments arg(rb_mKernel, rb_to_id(validation_fun), 3, argv);
+			VALUE result;
+			RubyThreadedCall call(&arg, &result);
+			wxThread::ExitCode code = call.Wait();
+			if(code)
+			{
+				return false;
+			}
 			if(result != Qnil && result != Qfalse)
 				return true;
 		}catch (const char* e) {
@@ -302,26 +312,67 @@ namespace Automation4 {
 			delete RubyProgressSink::inst;
 			RubyProgressSink::inst = new RubyProgressSink(progress_parent, false);
 			RubyProgressSink::inst->SetTitle(GetName());
-			RubyProgressSink::inst->Show(true);
 
 			// do call
 			RubyAssFile *subsobj = new RubyAssFile(subs, true, true);
-			VALUE sel = CreateIntegerArray(selected); // selected items
-			RubyObjects::Get()->Register(sel);
-			VALUE result = rbFunCall(rb_mKernel, rb_to_id(macro_fun), 3, subsobj->rbAssFile, sel, rb_int2inum(active));
-			RubyObjects::Get()->Unregister(sel);
-			if(result != Qnil && result != Qfalse)
+			VALUE *argv = ALLOCA_N(VALUE, 3);
+			argv[0] = subsobj->rbAssFile;
+			argv[1] = CreateIntegerArray(selected); // selected items;
+			argv[2] = INT2FIX(active);
+			RubyCallArguments arg(rb_mKernel, rb_to_id(macro_fun), 3, argv);
+			VALUE result;
+			RubyThreadedCall call(&arg, &result);
+			RubyProgressSink::inst->ShowModal();
+			wxThread::ExitCode code = call.Wait();
+			RubyProgressSink::inst = NULL;
+			if(code)
+			{
+				if(TYPE(result) == T_STRING)
+					throw StringValueCStr(result);
+				else throw "Unknown Error";
+			}
+			else if(result != Qnil && result != Qfalse)
 			{
 				subsobj->RubyUpdateAssFile(result);
 			}
+			delete subsobj;
 		} catch (const char* e) {
 			wxString *err = new wxString(e, wxConvUTF8);
 			wxMessageBox(*err, _T("Error running macro"),wxICON_ERROR | wxOK);			
 		}
-		RubyProgressSink::inst->script_finished = true;
 }
 
 
+	RubyThreadedCall::RubyThreadedCall(RubyCallArguments *a, VALUE *res)
+		: wxThread(wxTHREAD_JOINABLE)
+		,args(a), result(res)
+	{
+		int prio = Options.AsInt(_T("Automation Thread Priority"));
+		if (prio == 0) prio = 50; // normal
+		else if (prio == 1) prio = 30; // below normal
+		else if (prio == 2) prio = 10; // lowest
+		else prio = 50; // fallback normal
+		Create();
+		SetPriority(prio);
+		Run();
+	}
+
+	wxThread::ExitCode RubyThreadedCall::Entry()
+	{
+		int error = 0;
+		*result = rb_protect(rbCallWrapper, reinterpret_cast<VALUE>(args), &error);
+		if(RubyProgressSink::inst)
+		{
+			RubyProgressSink::inst->script_finished = true;
+			wxWakeUpIdle();
+		}
+		if(error) {
+			*result = rb_errinfo();
+			return (wxThread::ExitCode)1;
+		}
+		return (wxThread::ExitCode)0;		
+	}
+
 	// RubyFeatureFilter
 	RubyFeatureFilter::RubyFeatureFilter(const wxString &_name, const wxString &_description, 
 		int merit, VALUE _filter_fun, VALUE _dialog_fun)
@@ -363,19 +414,32 @@ namespace Automation4 {
 			delete RubyProgressSink::inst;
 			RubyProgressSink::inst = new RubyProgressSink(export_dialog, false);
 			RubyProgressSink::inst->SetTitle(GetName());
-			RubyProgressSink::inst->Show(true);
 	
 			RubyAssFile *subsobj = new RubyAssFile(subs, true/*modify*/, false/*undo*/);
-			VALUE result = rbFunCall(rb_mKernel, rb_to_id(filter_fun), 2, subsobj->rbAssFile, Qnil /* config */);
-			if(result != Qnil && result != Qfalse)
+			VALUE *argv = ALLOCA_N(VALUE, 2);
+			argv[0] = subsobj->rbAssFile;
+			argv[1] = Qnil; // config
+			RubyCallArguments arg(rb_mKernel, rb_to_id(filter_fun), 2, argv);
+			VALUE result;
+			RubyThreadedCall call(&arg, &result);
+			RubyProgressSink::inst->ShowModal();
+			wxThread::ExitCode code = call.Wait();
+			RubyProgressSink::inst = NULL;
+			if(code)
+			{
+				if(TYPE(result) == T_STRING)
+					throw StringValueCStr(result);
+				else throw "Unknown Error";
+			}
+			else if(result != Qnil && result != Qfalse)
 			{
 				subsobj->RubyUpdateAssFile(result);
 			}
+			delete subsobj;
 		} catch (const char* e) {
 			wxString *err = new wxString(e, wxConvUTF8);
-			wxMessageBox(*err, _T("Error running filter"),wxICON_ERROR | wxOK);			
+			wxMessageBox(*err, _T("Error running filter"),wxICON_ERROR | wxOK);
 		}
-		RubyProgressSink::inst->script_finished = true;
 	}
 
 	ScriptConfigDialog* RubyFeatureFilter::GenerateConfigDialog(wxWindow *parent)
@@ -422,8 +486,6 @@ namespace Automation4 {
 	{
 		float _progr = rb_num2dbl(progress);
 		RubyProgressSink::inst->SetProgress(_progr);
-		RubyProgressSink::inst->DoUpdateDisplay();
-		wxSafeYield(RubyProgressSink::inst);
 		return Qtrue;
 	}
 
@@ -431,7 +493,6 @@ namespace Automation4 {
 	{
 		wxString _t(StringValueCStr(task), wxConvUTF8);
 		RubyProgressSink::inst->SetTask(_t);
-		RubyProgressSink::inst->DoUpdateDisplay();
 		return Qtrue;
 	}
 
@@ -439,8 +500,6 @@ namespace Automation4 {
 	{
 		wxString _t(StringValueCStr(title), wxConvUTF8);
 		RubyProgressSink::inst->SetTitle(_t);
-		//wxSafeYield(RubyProgressSink::inst);
-		RubyProgressSink::inst->DoUpdateDisplay();
 		return Qtrue;
 	}
 
@@ -461,8 +520,6 @@ namespace Automation4 {
 		else args[1] = args[0];
 		wxString _m(StringValueCStr(args[1]), wxConvUTF8);
 		RubyProgressSink::inst->AddDebugOutput(_m);
-		RubyProgressSink::inst->DoUpdateDisplay();
-		wxSafeYield(RubyProgressSink::inst);
 		return Qtrue;
 	}
 
@@ -564,7 +621,8 @@ namespace Automation4 {
 		VALUE result;
 		result = rb_protect(rbCallWrapper, reinterpret_cast<VALUE>(&arg), &error);
 		if(error) {
-			//throw StringValueCStr(ruby_errinfo);
+			VALUE err = rb_errinfo();
+			throw StringValueCStr(err);
 		}
 		return result;
 	}
diff --git a/aegisub/auto4_ruby.h b/aegisub/auto4_ruby.h
index 7762e2dde..f5fa5b6b7 100644
--- a/aegisub/auto4_ruby.h
+++ b/aegisub/auto4_ruby.h
@@ -76,12 +76,12 @@ namespace Automation4 {
 		static int RubyUnparseTagData();
 		static int RubySetUndoPoint();
 
-		~RubyAssFile();
 	public:
 		void RubyUpdateAssFile(VALUE subtitles);
 		static VALUE AssEntryToRuby(AssEntry *e); // makes a Ruby representation of AssEntry
 		static AssEntry *RubyToAssEntry(VALUE ass_entry); // creates an AssEntry object from a Ruby representation
 		RubyAssFile(AssFile *_ass, bool _can_modify, bool _can_set_undo);
+		~RubyAssFile();
 
 		static RubyAssFile *raf;
 		VALUE rbAssFile;
@@ -245,6 +245,17 @@ namespace Automation4 {
 		RubyCallArguments(VALUE _recv, ID _id, int _n, VALUE *_argv);
 	};
 
+	// A single call to a Ruby function, run inside a separate thread.
+	// This object should be created on the stack in the function that does the call.
+	class RubyThreadedCall : public wxThread {
+	private:
+		RubyCallArguments *args;
+		VALUE *result;
+	public:
+		RubyThreadedCall(RubyCallArguments *args, VALUE *result);
+		virtual ExitCode Entry();
+	};
+
 	VALUE rbCallWrapper(VALUE arg);
 	VALUE rbExecWrapper(VALUE arg);
 	VALUE rbLoadWrapper(VALUE arg);
diff --git a/aegisub/auto4_ruby_assfile.cpp b/aegisub/auto4_ruby_assfile.cpp
index 4298390e9..dd7b78a4e 100644
--- a/aegisub/auto4_ruby_assfile.cpp
+++ b/aegisub/auto4_ruby_assfile.cpp
@@ -337,8 +337,8 @@ namespace Automation4 {
 	// If the first line is dialogue we leave header from the original (styles, info, etc)
 	void RubyAssFile::RubyUpdateAssFile(VALUE subtitles)
 	{
-		RubyObjects::Get()->Register(subtitles);
-		int size = rb_num2long(rb_funcall(subtitles, rb_to_id(rb_str_new2("size")), 0));
+		//RubyObjects::Get()->Register(subtitles);
+		int size = RARRAY(subtitles)->len;
 
 		if(size <= 0) return; // empty - leave the original
 		
@@ -378,7 +378,7 @@ namespace Automation4 {
 				rb_set_errinfo(Qnil);
 			}
 		}
-		RubyObjects::Get()->Unregister(subtitles);
+		//RubyObjects::Get()->Unregister(subtitles);
 	}
 	
 	int RubyAssFile::RubyParseTagData()
@@ -401,7 +401,6 @@ namespace Automation4 {
 
 	RubyAssFile::~RubyAssFile()
 	{
-		RubyObjects::Get()->Unregister(rbAssFile);
 	}
 
 	RubyAssFile::RubyAssFile(AssFile *_ass, bool _can_modify, bool _can_set_undo)
@@ -409,12 +408,8 @@ namespace Automation4 {
 		, can_modify(_can_modify)
 		, can_set_undo(_can_set_undo)
 	{
-		if(RubyAssFile::raf)
-			delete RubyAssFile::raf;	// delete previous if there is one
-		RubyAssFile::raf = this; // set pointer to this obj
 
 		rbAssFile = rb_ary_new2(ass->Line.size());
-		RubyObjects::Get()->Register(rbAssFile);
 
 		std::list<AssEntry*>::iterator entry;
 		int status;