No CollaborationOccurrences in Project Browser

[FR.]

When I create CollaborationOccurrences (as the instances of previously created Collaborations) these objects appear on the diagrams, but they don't show up in Project Browser.

Although any CollaborationOccurence can't be seen in Project Browser, it's possible to find out in which package it is placed in model: I can copy CollaborationOccurence object from one diagram and paste it onto another . It will be displayed there with a comment "from ..." naming the package it actually belongs to.

Of course, I can't move this object to another package because I don't have it in Project Browser.

So the question is: Is it desired behavior? If yes, then what's the logic?