Voice problem in portal 2 co_op

[mustymaster]

In portal 2's co_op mode, the microphones of both players are always open despite having push to talk key binded and activated. The only way to stop the open microphones is to enter a command line in conslole "voice_mute 1 and "voice_mute 2" to unless hear your partner's voice all the time or mute them entirely. please fix