Version: (using KDE 4.0.83)
Installed from: Ubuntu Packages
After login in the system tray plasmoid I have on the desktop stays empty until I resize it. Afterwards all icons (including new ones) are shown.
Another problem (I hope it's ok to not open up another bug report for this one):
when moving the system tray plasmoid the icons do not move with it. The icons "snap back" into the plasmoid when/if it is resized.
see also bug #164786
*** This bug has been marked as a duplicate of 164320 ***