GMS: ConcurrentModificationException in AckCollector.handleView()

We encountered the following CME exception on one of our production environment:

java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.remove(HashMap.java:860)
at java.util.AbstractCollection.retainAll(AbstractCollection.java:393)
at org.jgroups.util.AckCollector.handleView(AckCollector.java:85)
at org.jgroups.protocols.pbcast.GMS.installView(GMS.java:479)
at org.jgroups.protocols.pbcast.CoordGmsImpl.handleViewChange(CoordGmsImpl.java:460)
at org.jgroups.protocols.pbcast.GMS.up(GMS.java:711)
at org.jgroups.protocols.VIEW_SYNC.up(VIEW_SYNC.java:192)
at org.jgroups.protocols.pbcast.STABLE.up(STABLE.java:233)
at org.jgroups.protocols.UNICAST.up(UNICAST.java:299)
at org.jgroups.protocols.pbcast.NAKACK.handleMessage(NAKACK.java:861)
at org.jgroups.protocols.pbcast.NAKACK.up(NAKACK.java:693)
at org.jgroups.protocols.BARRIER.up(BARRIER.java:136)
at org.jgroups.protocols.VERIFY_SUSPECT.up(VERIFY_SUSPECT.java:167)
at org.jgroups.protocols.FD_ALL.up(FD_ALL.java:203)
at org.jgroups.protocols.FD_SOCK.up(FD_SOCK.java:308)
at org.jgroups.protocols.MERGE2.up(MERGE2.java:144)
at org.jgroups.protocols.Discovery.up(Discovery.java:263)
at org.jgroups.protocols.TP.passMessageUp(TP.java:1275)
at org.jgroups.protocols.TP.access$100(TP.java:49)
at org.jgroups.protocols.TP$1.run(TP.java:1178)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:650)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:675)
at java.lang.Thread.run(Thread.java:595)