As mentioned in JBEAP-9246 if MDB is marked as slow consumer then it's disconnected. However MDB immediately reconnects, this is to avoid of not having single MDB consuming messages on server. Disconnecting MDB as slow consumer will cause that all messages which MDB had in it's client buffer are returned to queue from which MDB was consuming and load balanced to all other consumer.

Behavior above should be documented in Configuring Messaging guide in chapter describing slow consumers.