According to this thread you aren't alone:
Poweramp hijacks the headset
controls(wired & BT) from all my other
media players... I use headset
controls with the stock mp3 player,
pandora, xiialive, & fm radio.. they
all surrender the headset controls
when not in use, but when I bring
poweramp in the mix the headset
controls only work with poweramp.. I
went into the headset options in
poweramp and disabled everything, that
stops the controls in poweramp, BUT
doesn't restore the headset controls
to the other players when I want to
use them...
but according to the last post by the dev this should fix it assuming you are running latest version (uninstalling would probably restore control as well):
Not exactly. I've made today a
workaround I mentioned above - so
unchecking Headset Buttons option in
PowerAMP now should properly redirect
next button presses to other players
(applies to 2.2 only). This will be
included in next minor release, coming
beginning of the next week.
Thanks for the report again.