Comment # 4 on bug 904097 from Stakanov Schufter

it would be my guess. Further I have found out the following:
if you use the keyboard combination in rapid sequence alt+ctrl+Fx then it
crashes.
If you go with the software switch of the plasmoid eYaSDP (enhanced yet another
shutdown plasmoid), then ... it doesn't happen. 
It did not occur to me that there would be a difference between switching VT
via KDE or via alt-ctrl-Fx. Is there? Or is it a matter of speed (you are
slower with the mouse)?

I will have maybe the possibility to "ping" it when I am in another location
next week. Here I have only my laptop, would not know how to test that here.