Workflow crashes when looping on a merge node

javax.servlet.ServletException: #{routingTaskActions.endTask(task)}: java.lang.UnsupportedOperationException
	at javax.faces.webapp.FacesServlet.service(FacesServlet.java:277)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.nuxeo.wss.servlet.BaseWSSFilter.doFilter(BaseWSSFilter.java:137)
...
Caused by: javax.faces.FacesException: #{routingTaskActions.endTask(task)}: java.lang.UnsupportedOperationException
	at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:118)
	at javax.faces.component.UICommand.broadcast(UICommand.java:387)
	at javax.faces.component.UIData.broadcast(UIData.java:938)
	at org.nuxeo.ecm.platform.ui.web.binding.alias.UIAliasHolder.broadcast(UIAliasHolder.java:86)
...
Caused by: javax.faces.el.EvaluationException: java.lang.UnsupportedOperationException
	at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:102)
	at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:102)
	... 77 more
Caused by: java.lang.UnsupportedOperationException
	at org.nuxeo.ecm.platform.routing.core.impl.GraphNodeImpl.cancelTasks(GraphNodeImpl.java:612)
	at org.nuxeo.ecm.platform.routing.core.impl.GraphRunner.recursiveCancelInput(GraphRunner.java:302)
	at org.nuxeo.ecm.platform.routing.core.impl.GraphRunner.runGraph(GraphRunner.java:208)
	at org.nuxeo.ecm.platform.routing.core.impl.GraphRunner.resume(GraphRunner.java:132)
	at org.nuxeo.ecm.platform.routing.core.impl.DocumentRouteElementImpl.resume(DocumentRouteElementImpl.java:88)
	at org.nuxeo.ecm.platform.routing.core.impl.DocumentRoutingEngineServiceImpl.resume(DocumentRoutingEngineServiceImpl.java:41)
	at org.nuxeo.ecm.platform.routing.core.impl.DocumentRoutingServiceImpl$2.run(DocumentRoutingServiceImpl.java:290)
	at org.nuxeo.ecm.core.api.UnrestrictedSessionRunner.runUnrestricted(UnrestrictedSessionRunner.java:156)
	at org.nuxeo.ecm.platform.routing.core.impl.DocumentRoutingServiceImpl.completeTask(DocumentRoutingServiceImpl.java:284)
	at org.nuxeo.ecm.platform.routing.core.impl.DocumentRoutingServiceImpl.endTask(DocumentRoutingServiceImpl.java:807)
	at org.nuxeo.ecm.platform.routing.web.RoutingTaskActionsBean.endTask(RoutingTaskActionsBean.java:169)
...