Parent link to an associated PA not works on plan view

Hello All,

I have an Project Area A associated to a Project Area B to trace some kind of workitens among then.

When I try to link some workitems from the plan view of Project Area B as children of a workitem at the Project Area A the combo box of PA´s is showned grayed.

If I link my workitem on Project Area B throught the tab Links its possible to select the Project Area A. The problem on that approach is that I have to link a dozen of workitens one-by-one

Is it a bug or considered "work as designed"?