Bug when completing a task (multiple ones are completed in same transaction)

So I have a use case where I had some hard times figuring out how it should be modeled.

Basically the way I modeled it in the end was with an event subprocess (sub execution) that could be triggered from three places in the process by go through a throwing signaling event. The event subprocess then contained a multiinstance user task.

The subprocess and one of the throwing events can be seen below:

So what happens here is that the event subprocess can be initiated multiple times through the process lifecycle which in this case means the user tasks can belong to the same subprocess execution or to another one. (I suspect this have to do with the bug we now are experiencing which I will explain below)

The error we are having is kind of intermittent, so I am having a hard time reproducing it in a test case.

What happens is that when one user completes one of the comment tasks, sometimes another comment task is also completed in that transaction. So somewhere in the engine its seems like the taskId are getting mixed up with the executionId or similar.

I will try to create a junit-test to reproduce this but it would be great to hear if anyone have an idea whats happening here?

No, not really. The only thing I can think of is concurrent throwing of the signal in multiple transactions, but even then I would expect an optimistic locking exception. A unit test would help a lot here, indeed.