Well basically I'm trying to solve a mystery Konrad.
I gave a click track to a drummer (the metronome in fact), 88 BPM on the project it seems with a set of headphones. All appeared working and nothing more about it was said again. When the session was over I thought I'd check the click to see if it was (more or less) in time (yes I should have done it during the session, schoolboy error, but the gig was short notice). Well the click was still there but it was NOT the same tempo that the drummer played. Also note there are no tempo changes in the project.
Now if it was the case the drummer was ignoring the tempo and creating his own then the guy is some sort of genius because he seems perfectly in time in another tempo whilst listening to a completely different tempo. Not only that the issue is not only in one project, but about 8 of them (2 songs across 8 or so takes).
Weird.