For example in 3.4.5 we see:
As a consumer I can depend on zookeeper with an exclude for org.jboss.netty#netty or I can let my transitive dep resolver pick a winner. This might be fine, except for those who might be using a more modern netty published under the newish io.netty groupId. With this twist you get both org.jboss.netty#netty;foo and io.netty#netty;bar on your classpath and runtime errors ensue from incompatibilities. unless you add an exclude against zookeeper (and clearly don't enable the zk netty nio handling.)
I propose that this is a pom bug although this is debatable. Clearly as currently packaged zookeeper needs netty to compile, but I'd argue since it does not need netty to run, either the scope should be provided or optional or a zookeeper-netty lib should be broken out as an optional dependency and this new dep published by zookeeper can have a proper compile dependency on netty.