It does but your characters mouth stops moving (which indicates that you're no longer transmitting sound). Also I've tried it with the other channels and your name in the bottom left disappears after a second and your character's mouth stops moving.
I've tried rebinding it and I've tried binding it to a different key.
I get the exact problem.
The problem is that it activates for a second and then instantly deactivates and I still haven't found a fix. When I proccess a suspect i'll usually take a picture of their crimes and bounty with my phone.
If you find a fix please let me know.