Hi,
after updating to Kubuntu 15.4. gtk-Programs can not show an icon at the system tray. I tried with pidgin, thunderbird and keepass2. (All in the version coming with kubuntu 15.4.)

• Is there a hint what I can do?
• Is it a bug of the new plasma?

Yours
Gonzo

Here is the answer to this question:
https://forum.kde.org/viewtopic.php?f=66&t=125465&p=333673&hilit=tray#p331512
Next time my search for answers will be more efficient.