Natty regression : built-in mic does not record

The build-in microphone of my Acer Aspire 4520 laptop does not record under Natty, though the usual white noise is still audible. I cannot test the on-line input as i haven't got any external mic.

Note that i have double checked all audio levels and input settings ;)

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: alsa-base 1.0.24+dfsg-0ubuntu1
ProcVersionSignature: Ubuntu 2.6.38-8.42-generic 2.6.38.2
Uname: Linux 2.6.38-8-generic x86_64
NonfreeKernelModules: nvidia
AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.23.
AplayDevices:
 **** List of PLAYBACK Hardware Devices ****
 card 0: NVidia [HDA NVidia], device 0: ALC268 Analog [ALC268 Analog]
   Subdevices: 1/1
   Subdevice #0: subdevice #0
Architecture: amd64
ArecordDevices:
 **** List of CAPTURE Hardware Devices ****
 card 0: NVidia [HDA NVidia], device 0: ALC268 Analog [ALC268 Analog]
   Subdevices: 1/1
   Subdevice #0: subdevice #0
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: rfm 1530 F.... pulseaudio
Card0.Amixer.info:
 Card hw:0 'NVidia'/'HDA NVidia at 0xf4480000 irq 18'
   Mixer name : 'Realtek ALC268'
   Components : 'HDA:10ec0268,10250127,00100003 HDA:11c11040,10250127,00100200'
   Controls : 11
   Simple ctrls : 8
Date: Wed Apr 27 17:36:04 2011
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Alpha amd64 (20110321)
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=es_DO:en_US:en
 LANG=es_DO.UTF-8
 SHELL=/bin/bash
SourcePackage: alsa-driver
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 05/14/2008
dmi.bios.vendor: Acer
dmi.bios.version: v1.3632
dmi.board.name: Mono
dmi.board.vendor: Acer, Inc.
dmi.board.version: Not Applicable
dmi.chassis.type: 1
dmi.chassis.vendor: Acer, Inc.
dmi.chassis.version: N/A
dmi.modalias: dmi:bvnAcer:bvrv1.3632:bd05/14/2008:svnAcer,inc.:pnAspire4520:pvrNotApplicable:rvnAcer,Inc.:rnMono:rvrNotApplicable:cvnAcer,Inc.:ct1:cvrN/A:
dmi.product.name: Aspire 4520
dmi.product.version: Not Applicable
dmi.sys.vendor: Acer, inc.