Yep and it may do it at a whim too, even moving across a room, I've had mine switch sites when in spectrum scan. I think perhaps he doesn't fully understand how the Unications work or how to actually program one for a FD or other public service situation where getting the call reliably is needed.Your choice, either change as @K9KLC suggests or live with symptoms you are experiencing. This is how they work.
It grabs a site from the list programmed with good decode, not necessarily the best signal or closest tower.