It seems that the "Deploy Ghost" keybind also doubles as the "toggle between team and fireteam chat channels" key, even though this is not listed anywhere in the keybind UI. Having rebound my Ghost to "G", it seems that pressing the letter "G", EVEN WHILE TYPING A MESSAGE, will trigger this behavior and change the target channel I am typing to. This means it's actually impossible for me to whisper anyone with the letter "G" in their name, or type any words containing G, without toggling to a different chat context.