Problem with Flag

When i join a battle in CTF (capture the flag) i can take the opponents flag but i can't give the flag to out base plate to score. When i drop the flag in the area of our base plate it says that i lost the flag.
when i'm playing the same game a second time (after time is ended) then my tank give the flag the the base plate. What can be the issue? it's very frustated to be able to take the falg but not to deliver it.