WS client deadlock with AsyncHttpClient

We use the WS client to perform potentially many web service requests in parallel. We now ran into an issue where the underlying AsyncHttpClient reaper threads deadlock (?). All reaper threads are in the following state:

AsyncHttpClient-Reaper WAITING on java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject 

As far as I can see, the situation is similar to the one described in http://stackoverflow.com/questions/20644160/using-the-play-ws-api-from-pure-scala-with-sbt

We are using Play 2.2.2 with Scala 2.10.4.