@echo44
Has this issue been resolved for you? I have received a brand new OB-6 today and am experiencing tuning issues as well:
Specifically, when holding a note, the pitch might shift up by ~25 cents after a while and back down again after a few more seconds. A while ago, I was using an older unit which I returned because a number of other issues, that seemed to show a similar behavior.
I have the suspicion that it might be a quantization issue with the temperature tables (such as switching between different sets of parameters when the measured temperature inside the unit slightly changes). The displayed temperature is a constant 47 degrees celsius. The firmware version is 1.6.8 (the used one I still had a few weeks ago was the currently downloadable version 1.6.6).
Edit: I have calibrated the unit a couple of times in warmed up condition but this did not change anything.