Studio XPS 13 can't switch output when muted - why?

Hello,

I recently purchased a Studio XPS 13 from Best Buy.  It's working great so far, with one exception that I'm hoping someone can help me out with. And my apologies in advance if this has already been addressed; I wasn't able to find it anywhere.

Anytime my computer is muted, it's impossible to switch between using the audio output jack and using the built-in speakers. For example, if it's muted then I plug in headphones or external speakers, after un-muting the plugged-in device doesn't function. If I pull the cord out of the jack the built-in speakers work fine, but nothing that's plugged in will work. The same thing happens if I mute the volume while something's plugged in (only the plugged in thing will work after unmuting).

I've found one solution, but it's somewhat convoluted. My computer uses IDT audio, and the IDT audio control panel has setting for two playback devices. The first is labeled "Speakers/Headphones," was set to default when I got the laptop, and the second is "Independent (R.T.C.) Headphones." If I'm experiencing the problem I described above, I can fix it by going into the audio control panel and pressing the "Test Speakers" button of the R.T.C. device. For whatever reason, even though that's not the device I'm using, it restores functionality.  Changing certain other settings in the menu works as well; pressing the test button is merely the simplest solution.

The first time this happened, I returned the laptop to the store and got a new one.  Unfortunately, it's happening on the new one as well, and seems to be a common problem on this laptop model.  I have (as far as I can tell) the most current drivers available. I'm using Windows Vista 64-bit with 4GB of DDR3 RAM, with a Core 2 Duo P8600 processor. I'd appreciate any help people can give, and can try to provide more information about the laptop if necessary.

Thanks in advance!