Users can only upvote five questions per proposal on Area 51, as is well known. It is probably less well known that you don't have to have followed a proposal to upvote or even propose questions.
What I didn't know until I tested it today is that there does not seem to be any limit in the number of downvotes a user may inflict on a proposal, even one they never committed to. I just successfully made (and then reversed) seven downvotes on questions on a proposal I am not following.
Bulk downvoting would probably be picked up by the abuse detectors but it does seem like a loophole that would allow users to throw sand in the wheels of a rival proposal to the o e they favor.
EDIT Please note that I am not referring to the per-day voting limits. The issue is that a user can only upvote five questions on a particular proposal, but can downvote all the the questions on that proposal. In the unlikely event there were more than 30 questions on a proposal, you could still downvote them all over several days. But you could only upvote five of them. This seems asymmetric.