to be able to run bind inside a vserver one needs to disable capabilities. this is currently only possible with USE=-threads, which is not the best thing to do
i will probably fix this myself in the next weeks if not even a comment to this problem is possible.
after studying the bind source it seems that thread support requires capabilities for whatever strange reason. although this does not fix the issue, i'm closing this one as invalid, since it seems to be an upstream limitation and no one cares enough to fix it.