Some thumbnails not shown/generated with tumbler-4.17.2, only after manual refresh

Starting with tumbler-4.17.1, some thumbnails in thunar do not get generated/shown until a manual refresh, or when re-entering the folder after generation. Reverting to tumbler-4.17.0 fixes this. Not sure if this is a bug in tumbler or thunar. Maybe it has to do with having different file types in a view, I will have to test this more thoroughly.

tumbler-4.17.2 works a bit better than 4.17.1 because with 4.17.1 thunar seems to try to regenerate some thumbnails that have already been generated.

I've tested this using current thunar master.