I have a new ASUS G55VW laptop and had the issue since purchase (some week ago). I always use headphones when listening to games/music. If I put the headphones in the jack the sound exits the headphones and the built-in speakers mutes (as expected). However, if I stop playing any sounds on my PC for some time (like 15 minutes), and then plays a sound, the sound will start exiting the built in laptop speakers instead - even though the headphones are still connected.
If I keep playing sound while the headphones are connected, the sound will exit those for hours (so far it has never switched from headphones to speakers while sound was playing)
It does not seem to be a hardware issue with the jack itself since it never changes output from headphones to built-in speakers as long as the sound is playing, but only if the sound pauses.
When sound starts to go to speakers, I need to reconnect the headphones to the 3.5-jack again.
Ive tried finding some settings in Windows to adjust this behavior with no success. Advise appriciated!