NSOutlineView MoveItemAtIndex Doesn't Revive

I have an NSOUtlineView (view-based) that is programmatically fully functional with drag and drop - i.e. I implemented all the correct methods and everything seems to work fine. Everything except the animation.

When I execute MoveItemAtIndex, line movements are not expected. However, the line moves because when I look up or down, the view is updated and the line is in its new place. I have confirmed that all input arguments are correct.

Also, when I submit an invalid "oldParent" element, the line insert animation works correctly! And if I sent an invalid element "newParent", the line delete animation works correctly! Needless to say, this bothers me - did I miss something regarding the MoveItemAtIndex function? The documents seem to be very small, everything seems to indicate that the animation should "just work."

I tried with and without beginUpdates / endUpdates, each time getting the same result.

Does anyone know if there is something that is not documented or hard to find regarding these animations?

thank