https://bugs.winehq.org/show_bug.cgi?id=46558
--- Comment #10 from BabbleBones@gmail.com --- Sure didn't fix the issue but it prodded the right spot!
Lots of pink textures in the UI where it should have been transparent and most importantly, the planet was utterly flat at a distance and crashed me, up close!
That's it! The 16 -> 8 bit is giving the grief and it's somewhere in windowscodecs or libpng itself.