Just to be clear on the issue:
The problem as I see it is only that the manual and SFI states that T1 is used for locking a target, while in game one have to use TV, so its no big issue in that sense.
I don't have the issue with unlocking the target after. From the OP side, this might have something to do with having to press T0 after locking a target with TV, otherwise you are flying around with TV permanently pressed and the radar will consistently try to lock something.
If you have a lock on a target and the radar trigger in T0 position, the lock will remain as long as the target is in certain parameters of the radar elevation/azimuth. If the target is outside those parameters, the radar will return to normal (unlocked) mode again after a few seconds.