When calling BeanSession.save(Subject)

com.google.gwt.user.server.rpc.UnexpectedException: Service method 'public abstract java.lang.String edu.uiuc.ncsa.dse.client.service.gwtrpc.WorkflowRemoteService.submitExecution(edu.uiuc.ncsa.cet.bean.dse.PublishedWorkflowBean,java.lang.String,java.lang.String,java.util.Map,java.util.Map) throws edu.uiuc.ncsa.dse.client.ui.workflow.WorkflowSubmitException' threw an unexpected exception: java.util.ConcurrentModificationException
at com.google.gwt.user.server.rpc.RPC.encodeResponseForFailure(RPC.java:360)
at com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:546)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.processCall(RemoteServiceServlet.java:164)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.doPost(RemoteServiceServlet.java:86)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
at org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:857)
at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:565)
at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1509)
at java.lang.Thread.run(Unknown Source)
Caused by: java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextEntry(Unknown Source)
at java.util.HashMap$KeyIterator.next(Unknown Source)
at org.tupeloproject.kernel.SubjectSession.saveSubjects(SubjectSession.java:300)
at org.tupeloproject.kernel.SubjectSession.save(SubjectSession.java:274)
at org.tupeloproject.kernel.BeanSession.save(BeanSession.java:1497)
at org.tupeloproject.kernel.BeanSession.save(BeanSession.java:1388)
at org.tupeloproject.kernel.BeanSession.save(BeanSession.java:1374)
at edu.uiuc.ncsa.dse.server.workflow.WorkflowExecution.submitExecution(WorkflowExecution.java:197)
at edu.uiuc.ncsa.dse.server.WorkflowRemoteServiceImpl.submitExecution(WorkflowRemoteServiceImpl.java:396)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:527)
... 16 more