Comment 356 for bug 439448

It may be a factor, but as I said earlier (what, you didn't reread the 355 comments ? ;-) I managed to reproduce the issue (especially in the bottom panel, next to the "show desktop" applet) from a clean user profile, with the default set of applets.

What was particularly striking was the fact that re-creating afterwards exactly the same set of applets made the issue more difficult to occur. From the "default set", I could force it to happen by "killing" the panel from the terminal a couple of times.