I just stumbeled over this new version of BDBMapVote for UT in BDB's Forum. I never saw it on a server yet, I also don't know when/if it was officially released.
http://www.fileplanet.com/dl.aspx?/planetunreal/BDBUnreal/bdbmapvote303_nodocs.zip
But the good thing about this version: Admins can new force a map switch although the map may be locked in the map cycle.