Bad Company 2's beta was based on a different code base than that of the final, released game. The "Beta" had bugs that needed to be patched separate from the final code they were working on at the time.
I suspect that this is the same, considering that you're playing on the same map that was in the Alpha.
Additionally, this is a BETA people, not a demo. Expect that some things will be broken. Let DICE know about it in a courteous manner and get on with your play.