haha, no worries if you find a better tool, just be sure to let me know about it so I can use it too! :)
I've actually used both mtpaint and Grafx2 and like them both! Grafx2 in particular is designed with indexed palettes in mind, so it does a much better job with them then GIMP imho.
btw, found the garbled pixels bug. It did have something to do with OpenGL and 'odd' image sizes. Although, as it turns out, not 'odd' as is in 'not divisible by 2' but 'odd' as in 'doesn't result in pixel data that perfectly aligns to 4 byte chunks'. I've got a fix for it, hoping to look more into the 'palette loading out of order' bug and then roll out a bug fixed build soon.
thanks again for your patience and providing demonstration files!