I found another problem in Black Ops II Treyarch. Sometimes when using the mute all players but party feature it mutes some of my party members. That isn't supposed to happen and does the opposite of what the feature is meant to do. This is not meant to be a complaint but rather feedback so that you can fix this issue in a future patch.
This is one of several party bugs that has been present since the beginning of the game. I doubt they will be fixed this late in the game. Would be nice though.
Happens to all of us, but at least we have the option to mute all.