If you have priority enabled, it will switch during a conversation.
I have a zone set up with local FD.
Position 1 is dispatch, ops 1, ops 2 and so on. It scans them.
Position 2 is Dispatch only.
Position 3 is Ops 1, Ops 2, Ops 3, Dispatch.
I have them in that order so if a fire call goes out and i want to listen i can go to Position 3 and the ops channels will have higher priority. So if Dispatch is talking and they talk on Ops 1, Ops 1 will then be the higher priority and pass audio.