usually symptoms of ballhead creep will be described like:think the way he painted it, seemed like ballhead creep. well , at least to me.
in any case, even people complain about markins and RRS creeping, and those are relatively expensive already...
http://forums.dpreview.com/forums/readflat.asp?forum=1032&message=36141251&changemode=1
so it *is* a common problem, and i won't just dismiss it as a possible explanation.
if indeed there is some play as TS describe, i'm not quite sure if this is necessarily the definite problem. the only way to know for sure is to try to resolve the play and see if this problem continues. for all we know, maybe it's a bit of both.
"I frame my shot through the viewfinder and lock the ballhead. When I release my grip on the camera, the view through the viewfinder moves a little/lot"
If TS describe that he can tilt the camera up by a bit, and also mentions a gap between plate and batt grip, I would not be so quick to jump to the 'ballhead creep' conclusion either.