Running Xubuntu 12.10 and current stable bitcoin from ppa:bincoin/bitcoin
First time I open the menu is "caged" but to big. Once I hover it it starts to overlay the items surrounding it it overlays the entire menu. Like this:

I tryed to use the other Icon that comes with bitcoin, /usr/share/pixmaps/bitcoin32.xpm that is smaller but still to big for the XFCE menu. I guess they are supposed to resize, but even if, the /usr/share/pixmaps/bitcoin80.xpm should not used by default for XFCE then.
Other icons in the pixmaps folder are 32x32 and are displayed correctly not sure why the Bitcoin icon not resizes.