That's definitely a bug. Scheduled (or any other kind of) tasks registered by a deployment should be cancelled and removed on undeploy.
Please file an issue at https://issues.jboss.org/browse/WFLY. Thanks.
1. Design choice, executors are shared among deployments and deployments are responsible for canceling their "futures".
2. It's a bug, yet already reported, and fix should be merged soon, meanwhile you need to use that Trigger workaround.
Thank you for your reply. Unfortunately, the fix has not been merged into wildfly 8.2, just into master, so I'll need to maintain the workaround.