I'll admit I'm a fan of Windows Classic Theme.
However, Corel Photo-PAINT doesn't play nice with certain dialogs in the theme, even though this theme has been officially released by Microsoft as part of their operating system.
One that's been a problem for many versions now is the Batch Process dialog (found under File | Batch Process). Try to load more than one image, and you'll see this:
In aero mode, it will work as expected. I've notified Corel about this, to no avail, multiple times.
Another error in Windows Classic Theme? Writing a file to disk can assign the wrong extension. No, you haven't been going crazy if you've seen this before.
Click on the image below for a clearer version:
