The new Multiop support added under zookeeper-965 fails every single time if the multiop is submitted to a non-leader in quorum mode. In standalone mode it always works properly and this bug only presents itself in quorum mode (with 2 or more nodes). After 12 hours of debugging (sigh) it turns out to be a really simple fix. There are a couple of missing case statements inside FollowerRequestProcessor.java and ObserverRequestProcessor.java to ensure that multiop is forwarded to the leader for commit. I've attached a patch that fixes this problem.
It's probably worth nothing that zookeeper-965 has already been committed to trunk. But this is a fatal flaw that will prevent multiop support from working properly and as such needs to get committed to 3.4.0 as well. Is there a way to tie these two cases together in some way?