Console shows "HTTP Status 500" error message when process definition contains fork

(This might be related to JBPM-2467)
When deploying a process that contains a fork to two tasks that are assigned to the same user, the console doesn't show the process instance and displays a "HTTP Status 500" error message when trying to access the task list. The same process runs fine and produces the expected results in a unit test. I'll attach a screenshot of the error message, an image of the process, the jpdl file and the unit test.