I've been looking around to see if anyone has ever reported this fact but i haven't found anything so i'll do it...
It seems that the Horde faction can exploit the gates that open when the battleground begins. I don't know how, but i occasionally see horde players get out of the spawn area before the battleground begins and prepare the spawn trap which is very frustrating. I hope you can investigate more, try to figure out what allows them to exploit the gates and fix it.
Thanks.