Dear Stig, Stewart, Harry, BEAR, mrclem, Drew, Nousaine,

Thank you all for your input! I really learned something!

It's good to hear that I can exclude my rig *per se* as a
cause of unstable imaging.

Since I am not familiar with recording/mixing procedures the
notion that a singer's movement in front of the microphone
might be the cause was rather surprising to me. I'll keep it
in my mind, though, when comparing different CDs next time.

My strongest suspicion was indeed on the interference of
direct and reflected sound. I actually bought a copy of F.
Alton Everest's "The master handbook of acoustics" a few
weeks ago to learn more about this subject, but I made it
only to the first couple of chapters yet... I will read more
and consider lateral reflection damping. However, this might
be an issue for my wife ;-)

Cheers,
Franco