"KeyError" suddenly appears after moving a limitswitch

Hey guys!
My linuxcnc / probebasic started to show a weird behaviour today.
After I start the system and home the machine, I get a popup saying "KeyError" _everytime_ when I jog any of the axes.
I can ignore that message, but it comes back everyime I jog again (no matter if via keyboard, softkey or pendant).

BUT - what I found out... as soon as I zero one of the axes (or all three), the error is gone.
I have not changed anything in my (software) config the last week, BUT I have modified my x axis yesterday and therefore moved the limitswitch a bit. 
Can this somehow be related? The popup says somewthing with "...active.WCSoffset..."... maybe some cached value doesnt fit anymore after I moved that switch?


Thx in advance!

Python's error messages are so unhelpful.



Did you change anything?