In maps such as Ow box, minecarts are used as bow targets to trigger redstone. As of right now spectators are able to break the minecarts, triggering the redstone.

Possibly a SportBukkit or perhaps a permissions issue.

Shouldn't be SportBukkit causing it. How are they being broken? Entity damage events are being cancelled, and minecarts are entities. Not sure. We will look into it. Thanks, paranormalcow.