ConcurrentModificationException

[liborw]

Sometime I'm getting following error when using rosjava_actionlib on the KUKA IIWA Robot,

Stopping task due the following error:
java.util.ConcurrentModificationException 
at java.util.HashMAP$HashIterator.nextEntry(UnknownSource)
at java.util.HashMap$ValuerIterator.next(UnknownSource)
at com.github.rosjava_actionlib.ActionServer.sendStatusTick(ActionServer.java:257)
at com.github.rosjava_actionlib.ActionServer$1.run(ActionServer.java:139)
at java.util.TimerThread.mainLoop(Unknown Source)
at.java.util.TimerThread.run(Unknown Source)

Any Idea what might be wrong?