System info :

HP Probook 450 G1
OS : Manjaro KDE 17.1.11 64bit
KDE Plasma version : 5.13.4
Kernel version : 4.14.60-1-MANJARO

When I click on any icons in system tray like (Volume - Networks - Bluetooth - Battery and brightness ....etc) , it opens the show-hidden-icons menu.

This bug is so annoying, and I stopped using KDE for few months and when I tried to use it again, this bug still exists!

This a picture to explain the bug :

https://s33.postimg.cc/ujad1lzbz/Screenshot_20180814_200023.png

Cannot reproduce and bet that you will not see that behaviour with a new user. Once that is confirmed we know that it is something in your home directory causing the problem. However, I looked for a systrayrc file or some such but found nothing.

Hence:

1. Create a new user
2. See whether you can replicate the behaviour
3. If not, find out which file is responsible for systray behaviour and delete
4. If behaviour persists, check Manjaro forum for solutions

Sorry I cannot be of more help and best of luck.

EDIT:
One other cause, however unlikely, could be a non-standard systray widget.

I chose to start with an empty session from start up and shutdown settings, and my issue stopped for now.