cannot set WPOS (grblHAL, Teensy)

[tretbootfahrer]

Hi all.

I cannot set WPOS in bCNC with grblHAL running on Teensy. WPOS and MPOS always show the same numbers.
I was suspecting the $10 setting in grblHAL and tried $10=1, $10=3 (as recommended for bCNC), even $10=2, no difference. Machine is homing OK and I don't see any other issues at the moment.

Previously the machine was running OK on grbl (arduino board). I upgraded to grblHAL with Phil Barrett's teensy board and took the settings I was using on the grbl/Arduino.
Do I have to compile grblHAL with compatibility levels for it to work with bCNC? The bCNC homepage mentions:

"Compatibility level" settings which have to be correctly configured
....but does not say what is "correct" for bCNC?

I'm lost, hoping for help. Thank you.

Stefan