Can only confirm this issue.
Target OS Windows 7 x64, driver version 4.0.2.1017.
After some investigation and playing around:
Disbaled all other recording devices (soundcard line-in, mic etc.), set Microphone USB Camera-B4.04.27.1 as default device.
Still have issue.
Another thing to think about:
Mic gain Level on Levels tab of Microphone USB Camera-B4.04.27.1 Properies sheet are locked on +6.0 db (even if it is functioning ), can not change it, the only option available here is mute on/off.
No other application started ( clean restart, avast antivirus only started automaticaly, Realtek HD Audio manager (my soundacrd control center) removed from autostart (suspected concurrency issue, but that was not))
As result:
Sometimes (does not found exact reason, mainly after reboot or hybernate) mic stops functioning. Till now the only way to get it back is unplug/plug camera again.
As far as i see alot of guys having such troubles, probably its time to workaround ???
As for me , i am ready to provide any help by performing any suggested tests and post any possible logs if necessary.