What I implemented is that join will terminate all left executions only when join activity will be completed, meaning that all or defined by multiplicity attribute execution have reached join node. So if I got it right this is what discriminator pattern is about?! (Please correct me if I am wrong).
In my opinion, process that you described could be quite common so there is rather high probability that end users will encounter it. I would say that it needs to be fixed in 4.4.