Mmmmmh. Yeah, I could change the code of "DisplayObject.setRequiresRedraw" so that it tries to get the frameID from the stage instead.
On the other hand, it is a good idea to call "setCurrent" whenever you've got multiple Starling instances and access Starling objects from a timer (or any other callback that's not initiated by the Starling loop). In this case, such a fix would let you get away with not doing it, but there are countless other places where it's necessary.
The problem is that "setRequiresRedraw" is a method that's called really often, and that other route of getting to the frameID is not the fastest one. Thus my hesitation.