@LadySmirk
It may be worth looking at this thread if you are seeking updated information: http://answers.ea.com/t5/Bugs-Issues/Turf-Takeover-counter-not-showing-correct-number-of-people-in/m-p/5264267#U5264267
It is indeed a bug when the incorrect amount of characters are detected in the area (usually putting it to zero thus ending OVERTIME).
Sorry but I can not pin point the cause: whether it is the lack of properly tracking of data by the game (common online problem) or just faults in the area's range. It is likely one of these two though it could be an entirely different reason to why this occurs (such as a way to turn off the "you are in the zone" flag of some kind).
-VoltScience: Exposition Mage