Unable to use front mic on Ubuntu 9.10

The front mic input is not working (volume seems to be very low).
In alsamixer I'm unable to modify Mic Boost or to set Mic Front Input to On (it is Off).
Initialy I had ubuntu 9.10 upgraded from 9.04 and Front Mic input was working.
But recently I have made a clean install of 9.10 and I got this problem with front Front Mic.
If I plug the headset in the rear input the Mic is working fine.
Is this a bug or am I missing something here?

Thanks !

lspci -vv | grep Audio
00:04.0 Multimedia audio controller: nVidia Corporation CK804 AC'97 Audio Controller (rev a2)

chipset shown in alsamixer: Realtek ALC850

amixer:

Simple mixer control 'Master',0
  Capabilities: pvolume pswitch pswitch-joined
  Playback channels: Front Left - Front Right
  Limits: Playback 0 - 31
  Mono:
  Front Left: Playback 31 [100%] [0.00dB] [on]
  Front Right: Playback 31 [100%] [0.00dB] [on]
Simple mixer control 'Master Mono',0
  Capabilities: pvolume pvolume-joined pswitch pswitch-joined
  Playback channels: Mono
  Limits: Playback 0 - 31
  Mono: Playback 0 [0%] [-46.50dB] [off]
Simple mixer control 'PCM',0
  Capabilities: pvolume pswitch pswitch-joined
  Playback channels: Front Left - Front Right
  Limits: Playback 0 - 31
  Mono:
  Front Left: Playback 27 [87%] [6.00dB] [on]
  Front Right: Playback 27 [87%] [6.00dB] [on]
Simple mixer control 'Surround',0
  Capabilities: pvolume pswitch
  Playback channels: Front Left - Front Right
  Limits: Playback 0 - 31
  Mono:
  Front Left: Playback 31 [100%] [0.00dB] [on]
  Front Right: Playback 31 [100%] [0.00dB] [on]
Simple mixer control 'Surround Jack Mode',0
  Capabilities: enum
  Items: 'Shared' 'Independent'
  Item0: 'Independent'
Simple mixer control 'Center',0
  Capabilities: pvolume pvolume-joined pswitch pswitch-joined
  Playback channels: Mono
  Limits: Playback 0 - 31
  Mono: Playback 31 [100%] [0.00dB] [on]
Simple mixer control 'LFE',0
  Capabilities: pvolume pvolume-joined pswitch pswitch-joined
  Playback channels: Mono
  Limits: Playback 0 - 31
  Mono: Playback 31 [100%] [0.00dB] [on]
Simple mixer control 'Line',0
  Capabilities: pvolume pswitch pswitch-joined cswitch cswitch-exclusive
  Capture exclusive group: 0
  Playback channels: Front Left - Front Right
  Capture channels: Front Left - Front Right
  Limits: Playback 0 - 31
  Front Left: Playback 27 [87%] [6.00dB] [off] Capture [off]
  Front Right: Playback 27 [87%] [6.00dB] [off] Capture [off]
Simple mixer control 'CD',0
  Capabilities: pvolume pswitch pswitch-joined cswitch cswitch-exclusive
  Capture exclusive group: 0
  Playback channels: Front Left - Front Right
  Capture channels: Front Left - Front Right
  Limits: Playback 0 - 31
  Front Left: Playback 26 [84%] [4.50dB] [on] Capture [off]
  Front Right: Playback 26 [84%] [4.50dB] [on] Capture [off]
Simple mixer control 'Mic',0
  Capabilities: pvolume pvolume-joined pswitch pswitch-joined cswitch cswitch-exclusive
  Capture exclusive group: 0
  Playback channels: Mono
  Capture channels: Front Left - Front Right
  Limits: Playback 0 - 31
  Mono: Playback 28 [90%] [7.50dB] [off]
  Front Left: Capture [on]
  Front Right: Capture [on]
Simple mixer control 'Mic Boost (+20dB)',0
  Capabilities: pswitch pswitch-joined
  Playback channels: Mono
  Mono: Playback [on]
Simple mixer control 'Mic Front Input',0
  Capabilities: pswitch pswitch-joined
  Playback channels: Mono
  Mono: Playback [off]
Simple mixer control 'Mic Select',0
  Capabilities: enum
  Items: 'Mic1' 'Mic2'
  Item0: 'Mic2'
Simple mixer control 'Video',0
  Capabilities: cswitch cswitch-exclusive
  Capture exclusive group: 0
  Capture channels: Front Left - Front Right
  Front Left: Capture [off]
  Front Right: Capture [off]
Simple mixer control 'Phone',0
  Capabilities: pvolume pvolume-joined pswitch pswitch-joined cswitch cswitch-exclusive
  Capture exclusive group: 0
  Playback channels: Mono
  Capture channels: Front Left - Front Right
  Limits: Playback 0 - 31
  Mono: Playback 23 [74%] [0.00dB] [off]
  Front Left: Capture [off]
  Front Right: Capture [off]
Simple mixer control 'IEC958',0
  Capabilities: pswitch pswitch-joined cswitch cswitch-joined
  Playback channels: Mono
  Capture channels: Mono
  Mono: Playback [on] Capture [off]
Simple mixer control 'IEC958 Playback AC97-SPSA',0
  Capabilities: volume volume-joined
  Playback channels: Mono
  Capture channels: Mono
  Limits: 0 - 3
  Mono: 3 [100%]
Simple mixer control 'IEC958 Playback Source',0
  Capabilities: enum
  Items: 'PCM' 'Analog In' 'IEC958 In'
  Item0: 'PCM'
Simple mixer control 'PC Speaker',0
  Capabilities: pvolume pvolume-joined pswitch pswitch-joined
  Playback channels: Mono
  Limits: Playback 0 - 15
  Mono: Playback 15 [100%] [0.00dB] [off]
Simple mixer control 'Aux',0
  Capabilities: pvolume pswitch pswitch-joined cswitch cswitch-exclusive
  Capture exclusive group: 0
  Playback channels: Front Left - Front Right
  Capture channels: Front Left - Front Right
  Limits: Playback 0 - 31
  Front Left: Playback 28 [90%] [7.50dB] [off] Capture [off]
  Front Right: Playback 28 [90%] [7.50dB] [off] Capture [off]
Simple mixer control 'Mono Output Select',0
  Capabilities: enum
  Items: 'Mix' 'Mic'
  Item0: 'Mix'
Simple mixer control 'Capture',0
  Capabilities: cvolume cswitch cswitch-joined
  Capture channels: Front Left - Front Right
  Limits: Capture 0 - 15
  Front Left: Capture 15 [100%] [22.50dB] [on]
  Front Right: Capture 15 [100%] [22.50dB] [on]
Simple mixer control 'Mix',0
  Capabilities: cswitch cswitch-exclusive
  Capture exclusive group: 0
  Capture channels: Front Left - Front Right
  Front Left: Capture [off]
  Front Right: Capture [off]
Simple mixer control 'Mix Mono',0
  Capabilities: cswitch cswitch-exclusive
  Capture exclusive group: 0
  Capture channels: Front Left - Front Right
  Front Left: Capture [off]
  Front Right: Capture [off]
Simple mixer control 'Channel Mode',0
  Capabilities: enum
  Items: '2ch' '4ch' '6ch' '8ch'
  Item0: '2ch'
Simple mixer control 'Duplicate Front',0
  Capabilities: pswitch pswitch-joined
  Playback channels: Mono
  Mono: Playback [off]
Simple mixer control 'External Amplifier',0
  Capabilities: pswitch pswitch-joined
  Playback channels: Mono
  Mono: Playback [on]