diff --git a/src/gfx/generated_image.hpp b/src/gfx/generated_image.hpp
index a28c3174..e4e242dd 100644
--- a/src/gfx/generated_image.hpp
+++ b/src/gfx/generated_image.hpp
@@ -45,7 +45,7 @@ class GeneratedImage : public ScriptValue {
 	/// Equality should mean that every pixel in the generated images is the same if the same options are used
 	virtual bool operator == (const GeneratedImage& that) const = 0;
 	inline  bool operator != (const GeneratedImage& that) const { return !(*this == that); }
-
+	
 	/// Can this image be generated safely from another thread?
 	virtual bool threadSafe() const = 0;
 	
@@ -64,8 +64,8 @@ class LinearBlendImage : public GeneratedImage {
 	virtual Image generate(const Options& opt) const;
 	virtual ImageCombine combine() const;
 	virtual bool operator == (const GeneratedImage& that) const;
-
-	virtual bool threadSafe() const {return true;}
+	
+	virtual bool threadSafe() const { return true; }
   private:
 	GeneratedImageP image1, image2;
 	double x1, y1, x2, y2;
@@ -82,8 +82,8 @@ class MaskedBlendImage : public GeneratedImage {
 	virtual Image generate(const Options& opt) const;
 	virtual ImageCombine combine() const;
 	virtual bool operator == (const GeneratedImage& that) const;
-
-	virtual bool threadSafe() const {return true;}
+	
+	virtual bool threadSafe() const { return true; }
   private:
 	GeneratedImageP light, dark, mask;
 };
@@ -99,8 +99,8 @@ class CombineBlendImage : public GeneratedImage {
 	virtual Image generate(const Options& opt) const;
 	virtual ImageCombine combine() const;
 	virtual bool operator == (const GeneratedImage& that) const;
-
-	virtual bool threadSafe() const {return true;}
+	
+	virtual bool threadSafe() const { return true; }
   private:
 	GeneratedImageP image1, image2;
 	ImageCombine image_combine;
@@ -117,8 +117,8 @@ class SetMaskImage : public GeneratedImage {
 	virtual Image generate(const Options& opt) const;
 	virtual ImageCombine combine() const;
 	virtual bool operator == (const GeneratedImage& that) const;
-
-	virtual bool threadSafe() const {return true;}
+	
+	virtual bool threadSafe() const { return true; }
   private:
 	GeneratedImageP image, mask;
 };
@@ -151,8 +151,8 @@ class PackagedImage : public GeneratedImage {
 	{}
 	virtual Image generate(const Options& opt) const;
 	virtual bool operator == (const GeneratedImage& that) const;
-
-	virtual bool threadSafe() const {return true;}
+	
+	virtual bool threadSafe() const { return true; }
   private:
 	String filename;
 };
@@ -167,8 +167,8 @@ class BuiltInImage : public GeneratedImage {
 	{}
 	virtual Image generate(const Options& opt) const;
 	virtual bool operator == (const GeneratedImage& that) const;
-
-	virtual bool threadSafe() const {return true;}
+	
+	virtual bool threadSafe() const { return true; }
   private:
 	String name;
 };
@@ -182,8 +182,12 @@ class SymbolToImage : public GeneratedImage {
 	~SymbolToImage();
 	virtual Image generate(const Options& opt) const;
 	virtual bool operator == (const GeneratedImage& that) const;
-
-	virtual bool threadSafe() const {return false;}
+	
+	#ifdef __WXGTK__
+		virtual bool threadSafe() const { return false; }
+	#else
+		virtual bool threadSafe() const { return true; }
+	#endif
   private:
 	SymbolToImage(const SymbolToImage&); // copy ctor
 	String           filename;
diff --git a/src/gui/new_window.cpp b/src/gui/new_window.cpp
index 9c0c3eb7..fb5b5fe7 100644
--- a/src/gui/new_window.cpp
+++ b/src/gui/new_window.cpp
@@ -92,13 +92,13 @@ void NewSetWindow::OnOK(wxCommandEvent&) {
 
 void NewSetWindow::done() {
 	try {
-	StyleSheetP stylesheet = stylesheet_list->getSelection<StyleSheet>();
-	set = new_intrusive1<Set>(stylesheet);
-	set->validate();
-	EndModal(wxID_OK);
-	} catch (Error& e) {
-	handle_error(e);
-	throw; // We want to crash.
+		StyleSheetP stylesheet = stylesheet_list->getSelection<StyleSheet>();
+		set = new_intrusive1<Set>(stylesheet);
+		set->validate();
+		EndModal(wxID_OK);
+	} catch (const Error& e) {
+		handle_error(e);
+		EndModal(wxID_CANCEL);
 	}
 }
 
diff --git a/src/gui/set/window.cpp b/src/gui/set/window.cpp
index 4d59dc60..125635b8 100644
--- a/src/gui/set/window.cpp
+++ b/src/gui/set/window.cpp
@@ -173,8 +173,6 @@ SetWindow::~SetWindow() {
 	delete find_dialog;
 	// remove from list of set windows
 	set_windows.erase(remove(set_windows.begin(), set_windows.end(), this));
-	// stop updating
-	onBeforeChangeSet();
 }
 
 // ----------------------------------------------------------------------------- : Panel managment
diff --git a/src/script/image.hpp b/src/script/image.hpp
index 9060bf55..0493073c 100644
--- a/src/script/image.hpp
+++ b/src/script/image.hpp
@@ -47,7 +47,7 @@ class ScriptableImage {
 	}
 
 	/// Can this be safely generated from another thread?
-	bool threadSafe() const {return value != nullptr ? value->threadSafe() : false; }
+	inline bool threadSafe() const { return !value || value->threadSafe(); }
 	
   private:
 	OptionalScript  script;		///< The script, not really optional