IndexOutOfBoundsException when trace logging

Exception in thread "OOB-1,test-NodeE-13479" java.lang.IndexOutOfBoundsException: Index: 4, Size: 2
	at java.util.ArrayList.rangeCheck(ArrayList.java:653)
	at java.util.ArrayList.get(ArrayList.java:429)
	at org.jgroups.protocols.pbcast.NAKACK2.handleMessages(NAKACK2.java:868)
	at org.jgroups.protocols.pbcast.NAKACK2.up(NAKACK2.java:705)
	at org.jgroups.stack.Protocol.up(Protocol.java:425)
	at org.jgroups.protocols.TP.passBatchUp(TP.java:1600)
	at org.jgroups.protocols.TP$BatchHandler.run(TP.java:1820)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:745)

boolean added=loopback || buf.add(msgs, oob, oob? DUMMY_OOB_MSG : null);