ClusterPartition invokes the JGroups Channel.down(Event) method in one place (startService()). In JG 2.5, the signature on that method has changed from a void return to an object return. That causes issues if users attempt to upgrade the AS to 2.5 (see JGRP-449).

A simple way to leave the upgrade path open is to change this call to use reflection. Hacky, but the call happens just once per server start.