I tried 3 different dock stations :
2 x DELL Thunderbolt dock stations TB16 and WD19
1 x HP Replicant 3005 regular USB 

I plug my USB Mouse and USB Keyboard to the dock and boot the machine.

After reaching X (KDE plasma in my case) I get intermittent connection breaks
so 

a.) 3-5 seconds period when keyboard and mouse work  
followed by 
b.) 1-2 seconds period of powerdown (keyboard backlight and mouse led both shut
down)

and the loop of a) + b) goes on forever

This only happens if the dock was plugged in from cold boot.
The solution is to unplug and re-plug the dock while the laptop experiences
this issues and problem disappears until next coldboot.

This happens for about a year now since I bought the docks.