After doing some experimentation, I found that the problem seems to be occuring in bars that start with auto-hide on. If you turn auto-hide off, then go to the menu editor and go to the skin tab, by changing the skin to something else and back, you can get your skin back. After that, you can turn auto-hide on again, and things should be ok for a bit. I have found that after a bit, the white background problem will come back. But i haven't figured out the exact trigger that causes it yet.
-Scott MacDonald