Hum you should have done something wrong.
Streamtuner use mplayer as the default player.

Check in preference menu that you have the default settings :
stlaunch %q
stlaunchm3u %

Check that you have no alias for mplayer

Check that you use regular streamtuner 0.99.99-12 from
http://maemo.org/downloads/product/OS2008/streamtuner/