Found the source of the growing style file bug (and fixed it)

src/data/settings.cpp

@@ -16,6 +16,7 @@
 #include <util/platform.hpp>
 #include <util/io/reader.hpp>
 #include <util/io/writer.hpp>
+#include <util/delayed_index_maps.hpp>
 #include <wx/filename.h>
 #include <wx/wfstream.h>
 #include <wx/stdpaths.h>
@@ -218,7 +219,18 @@ IMPLEMENT_REFLECTION_NO_SCRIPT(Settings) {
 	REFLECT(export_options);
 }
 
+void Settings::clear() {
+	recent_sets.clear();
+	game_settings.clear();
+	stylesheet_settings.clear();
+	default_stylesheet_settings = StyleSheetSettings();
+	export_options.clear();
+}
+
 void Settings::read() {
+	// clear current settings, otherwise we duplicate vector elements
+	clear();
+	// (re)load settings
 	String filename = settingsFile();
 	if (wxFileExists(filename)) {
 		// settings file not existing is not an error

src/data/settings.hpp

@@ -171,6 +171,8 @@ class Settings {
   private:
 	/// Name of the settings file
 	String settingsFile();
+	/// Clear settings before reading them
+	void clear();
 	
 	DECLARE_REFLECTION();
 };

src/util/delayed_index_maps.hpp

@@ -32,6 +32,11 @@ IndexMap<Key,Value>& DelayedIndexMaps<Key,Value>::get(const String& name, const
 	return item->read_data;
 }
 
+template <typename Key, typename Value>
+void DelayedIndexMaps<Key,Value>::clear() {
+	data.clear();
+}
+
 // ----------------------------------------------------------------------------- : Reflection
 
 // custom reflection : it's a template class

src/util/index_map.hpp

@@ -148,6 +148,8 @@ class DelayedIndexMaps {
   public:
 	/// Get the data for a specific name. Initialize the map with init_with (if it is not alread initialized)
 	IndexMap<Key,Value>& get(const String& name, const vector<Key>& init_with);
+	/// Clear the delayed index map
+	void clear();
   private:
 	map<String, intrusive_ptr<DelayedIndexMapsData<Key,Value> > > data;
 	friend class Reader;