Hello!

I used to use shortcuts for frequently used actions but I've found that System Tray plasmoid does not:

I have Network Management and Device Notifier in System Tray and I want to bind shortcuts for them. But shortcuts are working only after I setting them up and they disappear after relogin...

Such behavior I see since I started using kde from v4.5.2

This is probably because the System Tray applet is setting the applets up freshly on each startup. I suggest filing a bug at bugs.kde.org. In the meantime, as a workaround, open System Tray settings, disable the two applets there, and then re-add them to the panel using Add Applets.

OK, have created bugreport:
https://bugs.kde.org/show_bug.cgi?id=260685