I, too have a N800 running a "clean" Diablo install. My Pidgin is the same revision and I don't have the Close button visible either.

Maybe some other application is pre-empting at a higher level? OM Weather, advanced-backlight, large-statusbar-clock or load-applet perhaps?

I accepted the OS2008 Feature upgrade (ver 4.2008.36-5)...could that be the difference?

Or maybe one of the more subtler libraries visible only in red pill mode?