Currently whenever a player is typing if they hit the voice activation key it will active their mic in the example of this being the V key this can happen quite commonly, perhaps and option to disable mic activation when game chat is open.

Fixed in 2.1.0 by 5780027.

Now by default you can't use Push-To-Talk in chat and sign menus.
There is no option to disable it, but if someone will ask for it, I'll add it.