Comment 21 for bug 462764

The problem with this machine is that the ALSA HDA implementation incorrectly decodes the list of available audio devices. The internal microphone and audio input jack end up as different channels on the same stream, rather than separate streams. You can fix it at the PulseAudio mixer level by turning one of these channels all the way off, but that doesn't work reliably because many different programs change the mixer settings (usually without asking you).

I was able to work around this problem on my 1410 by adding the following line to /etc/modprobe.d/alsa-base.conf:
options snd_hda_intel model=basic

Please post if this fix works for you.