diff --git a/src/transparency_gui.cpp b/src/transparency_gui.cpp
--- a/src/transparency_gui.cpp
+++ b/src/transparency_gui.cpp
@@ -125,8 +125,14 @@ public:
 		return pt;
 	}
 
-	virtual void OnInvalidateData(int data)
+	/**
+	 * Some data on this window has become invalid.
+	 * @param data Information about the changed data.
+	 * @param gui_scope Whether the call is done from GUI scope. You may not do everything when not in GUI scope. See #InvalidateWindowData() for details.
+	 */
+	virtual void OnInvalidateData(int data = 0, bool gui_scope = true)
 	{
+		if (!gui_scope) return;
 		for (uint i = TTW_WIDGET_BEGIN; i < TTW_WIDGET_END; i++) {
 			this->SetWidgetLoweredState(i, IsTransparencySet((TransparencyOption)(i - TTW_WIDGET_BEGIN)));
 		}