I'm also experiencing this on both a 12.04 clean install and another machine upgraded from 11.10. The icon is invisible, but can be activated by left/right clicking the space where the icon should be. If you change the desktop theme to High Contrast, you can plainly see a dark gray square where the icon should be.
I have also noticed that doing a killall unity-2d-panel will cause the pidgin icon to display properly, but this does not always work, and the problem reoccurs if pidgin is stopped and restarted.
I'm also experiencing this on both a 12.04 clean install and another machine upgraded from 11.10. The icon is invisible, but can be activated by left/right clicking the space where the icon should be. If you change the desktop theme to High Contrast, you can plainly see a dark gray square where the icon should be.
I have also noticed that doing a killall unity-2d-panel will cause the pidgin icon to display properly, but this does not always work, and the problem reoccurs if pidgin is stopped and restarted.