JBPM operation results in deadlock on MS SQL Server

Issue

I have a simple jBPM process with a wait state and a timer. Before the timer expires, we use the following code to force the token to move on:

        try {
            JbpmConfiguration jbpmConfiguration = JbpmConfiguration.getInstance();
            JbpmContext jbpmContext = jbpmConfiguration.createJbpmContext();

            ProcessInstance instance = jbpmContext.loadProcessInstanceForUpdate(processId);
            instance.signal();
        } finally {  
            jbpmContext.close();  
    }

Everything is working fine if I am running one instance, but if we trigger multiple process instances concurrently from multiple threads, this results in a database deadlock:

ERROR (WorkManager(2)-34) javax.ejb.EJBException: org.hibernate.exception.SQLGrammarException: 
      could not initialize a collection: [org.jbpm.graph.def.Node.exceptionHandlers#282]
...
Caused by: com.microsoft.sqlserver.jdbc.SQLServerException: Distributed transaction completed. Either enlist this session in a new transaction or the NULL transaction.
    at com.microsoft.sqlserver.jdbc.SQLServerException.makeFromDatabaseError(SQLServerException.java:197)
    at com.microsoft.sqlserver.jdbc.SQLServerStatement.getNextResult(SQLServerStatement.java:1493)
    at com.microsoft.sqlserver.jdbc.SQLServerPreparedStatement.doExecutePreparedStatement(SQLServerPreparedStatement.java:390)
    at com.microsoft.sqlserver.jdbc.SQLServerPreparedStatement$PrepStmtExecCmd.doExecute(SQLServerPreparedStatement.java:340)
    at com.microsoft.sqlserver.jdbc.TDSCommand.execute(IOBuffer.java:4575)
    at com.microsoft.sqlserver.jdbc.SQLServerConnection.executeCommand(SQLServerConnection.java:1400)
    at com.microsoft.sqlserver.jdbc.SQLServerStatement.executeCommand(SQLServerStatement.java:179)
    at com.microsoft.sqlserver.jdbc.SQLServerStatement.executeStatement(SQLServerStatement.java:154)
    at com.microsoft.sqlserver.jdbc.SQLServerPreparedStatement.executeQuery(SQLServerPreparedStatement.java:283)