Can you suggest any workarounds to avoid the bug, except going back to Tk 8.6.4?
e.g.
- removing/adding transparency, since the buggy changes address the alpha-channel (in our application, the image contents are under our control)
- reverting all changes to tkImgPNG.c, tkImgPhoto.c (we are deploying statically linked binaries, so modification of Tk is a viable option)?

Regards
Florian