Hello henripster,
This is a bit of a late reply, but what is your start gcode for the print? What slicing software are you using?
Look out for this "G1 Z5 F5000", it could be your culprit, unless that is the 'Zoffset' you speak off.
I would remove that line of code and see what happens, or set it to G1 Z0 F5000 if you feel so inclined.
Good luck.