Hmm. Ok, some more infos:

This seems to be related to the Vitreous skin which uses Aero in this area. Selecting different skins solves the issue. Changing back to Vitreous brings it up again.
However once when I changed back the skin there was no flickering until the next restart of MM.

I can't reproduce either.

I can't reproduce it, where do you set the rating from? I tried via the hover stars and the toolbar, but everything seems normal.

The status bar (x files to tag) isn't coming up. The whole bottom bar (EQ, transport buttons, progress bar, ratings, ...) flickrs.
This also happens when loading a new song.

It seems to update the bar because some song data changed. So the controls get redrawed.
I don't remember that this happened in MM3.

I'm using the default skin.

Probably indicating it's tagging the file with the new rating value.

Hey,
on my computer the bottom bar flickrs a few seconds when rating a song. (Win 7 Home x64, ATI HD 6xxx)

Christoph