I have the same case here, but this does not sound familiar to me, sorry. In all but the most extreme positions the light stays almost exactly where I put it, independant on rotation. You can see this too in the movie I posted
here around 2:40 and 3:50 - the light, once moved, pretty much stays where it is positioned.
Same with rotation: I can rotate the head of the light over an about ~160 degree angle from back to front. Assuming you're not an extreme critic who finds a 1mm displacement totally unacceptable it seems to me you might have a defective unit.