I no longer have a thumb viewing problem on my Mac, but if I get Painter, I expect to have a problem with that one, with their .riff extensions.   That's another reason I don't use Painter.  It is a pain in the neck as far as I'm concerned.  All the little inconveniences take the pleasure out of painting for me.

“Music is harmony, harmony is perfection, perfection is our dream, and our dream is heaven”
Henri Frederic Amiel