Here's a pic: http://rlworkman.net/xfpm-trayicon-misbehave.png This doesn't happen every time - in fact, it happens rarely enough that I had forgotten about it and thought it was something that had been fixed; last night was the first time I'd seen this since xfce4-panel 4.7.2 or some such. When a new icon is placed in the notification area, it starts out as a black box sometimes (this is *very* fast) and then changes to its normal icon. However, occasionally, it never changes - instead, the normal icon appears *in addition to* the black box. I originally thought xfce4-power-manager was causing this, because the first few times I encountered it (which was on an older panel release), right-clicking on the black box would bring up xfpm options. This time, however, right-clicking results in nothing. I included the panel's notification area prefs window in the screenshot in case that's useful.
Crap, I just noticed the report from cwickert. Sorry for the noise. However, maybe xfpm *is* at fault :) *** This bug has been marked as a duplicate of bug 7057 ***