Note that fix is not perfect, systematically make refcounting of all IDs assigned to node's id pointer, which breaks the 'do not refcount scene/object/text datablocks' principle... But besides that principle being far from ideal in general, it becomes pretty much impossible to apply when using //generic// ID pointer, unless we add some kind of type data to that pointer somehow. So for now, better to live with that, than having broken usercount.