Proper use of `deactivate-mark'?

[Thorsten Jolitz]

Hi List, 

in a function I switch from buffer A to buffer B, mark the
thing-at-point, do something with it, conditional on

  ,--------------------
  | (and
  |  (use-region-p) ...
  `--------------------


, then call `(deactivate-mark)' at the end of the function and switch
back to buffer A again.

But the next time I switch to buffer B, the mark that was region-end
before seems to be still active - the region between that mark and the
actual point position is highlighted also I did not set any new mark
again. 

Isn't that the appropriate use of `deactivate-mark'?
How can I make sure that no mark is active anymore when I'm done in
buffer B and switch back to buffer A?

-- 
cheers,
Thorsten