Sorry if it's a silly question, it just hit me: which GTK version are we using on OSX and Windows for 1.37 and before? As the default switched to 3.x, do we use that? If 1.37 is the first GTK3 release there, it might very well be that…
1.37 for Windows was still GTK2 and since it seems already to happen with 1.36, it might have a lot more causes :(.