Boundary event with cancelActivity=true doesn't cancel tasks in sub process it is attached to

Create a process comparable with the one in the attached picture: The process contains an Embedded SubProcess with a parallel gateway leading to two tasks. Attached to the Embedded SubProcess is a boundary error event. This event is triggered when the one task in the sub process causes a problem. Now even if the other task is active (executeWorkItem was called, but workItemCompleted has not been called) it is not canceled, abortWorkItem is not called. This situation can occur when we use User Tasks, certain implementation of Receive Tasks that temporarily release control of the thread or any task in which an Exception occurred which causes completeWorkItem not to be called. We would expect a call of abortWorkItem for each work item of the sub process that is currently active.