Comment 22 for bug 502223

This looks very similar to the issues in bug #460351 that you have already subscribed to. Unfortunately I am unsure as to what else you could try in order to resolve this issue. I would suggest adding the "model=auto" back to your alsa-base.conf so that your external mic will function again.

It might be a good idea to keep an eye on bug #460351 to see if any progress is made there. If you want to verify that you are having the same issues as mentioned in that bug report, try booting the Karmic live CD & see if you are having the same issues in a live desktop environment.

It may also be worth trying the Lucid daily image (use live boot option) as a lot of the recent alsa work has been incorporated into Lucid. The Lucid daily image can be downloaded from the link below:
http://cdimage.ubuntu.com/daily-live/current/

If you are having the same issues you described here when using the Lucid daily CD it may help others if you run "apport-collect -p alsa-base 502223" from within the Lucid live desktop environment.

I am also trying to debug this exact same issue (headphone jack sensing) on another laptop that uses a different model of intel HDA. This jack sensing issue may be more widespread than initially thought.