I have just tried out v4 beta and I can confirm this works now.

Indeed there is a super tiny surface there at the bottom of that fillet. Maybe it has to do with the way I made that fillet: I made a hard step first, like this:



Then I filleted the top edge and for the fillet radius I chose the height of that step by clicking to top corner and the bottom corner. Maybe that wasn't exact because of the curvature of the surface below. Or maybe I let it snap at the wrong point. :D