I have a Samsung Series 7 NP700-Z5A, which has a dual-purpose mic/headphone jack.
In both Ubuntu 12.04 and Windows 7, whenever I plug in my headphones the internal mic goes completely dead.
When the headphones aren't plugged in, the mic is fine.
The hardware is Realtek HD audio and the driver version 18.104.22.16828 (on Windows, at least).
I have an inkling that it thinks my headphones are a microphone, but there seems to be no option (in either OS) to adjust this.
Has anyone else experienced this? Very grateful for any advice.