5.1 sounds double when i use a headphone

[deandoe]

Hello,
At the moment i use BSplayer Pro 1.36 (build 825), everything works great (also the 5.1 ac3 etc). When i want to watch a movie at night i often use a headphone (Sennheiser HD 212 Pro), when i do this i change my main Ac97 audio-configuration (on-board soundcard) from 5.1 to stereo when i then listen to a 5.1 movie with BSplayer the voices are kind of double... you hear like twice the voicechannal with a millisecond delay between it. Does somebody has the same problem? Or does anybody has the answer to this. (When i use Media Player Classic instead no double voice there)
Dean

Ps. sorry for my bad english...