Please report this thread along with all the other non-official ESL threads that should be locked. Thank you.
This happens because once it locks on there is 1 or 2 seconds of tolerance before the lock on breaks, to avoid random branches or infantry forcing you to wait all the seconds to stablish the lock on again. It's not a bug, it's intended EDIT: Fixed previous bad spelling and such things
Given that it's an Empire Specific Launcher and needs things like this to make it better than just another Annihilator, great point.