There are no solid black images in the theme whatsoever...I change EVERYTHING top to bottom that can possibly be modified in a theme so I'm sure of that. If you've been messing with the alignment properties for one of the image files in StyleBuilder, ResEdit, etc. however, it can result in a solid black box where the image file should appear (left alignment overlapping right, top overlapping bottom, etc.). Try setting the alignment properties back to their original settings and that should do the trick.
No need, my friend, I've added a couple of extra pixels of spacing to the toolbar/toolbar split.pngs that should take care of the problem. I use Firefox with Opera as a second choice so sometimes I don't catch IE misalignments...but the extra padding should take care of it. Enjoy!