Hi Burr, yes the algorithm used for face movement won't work on those cases.

When this face is moved:



The resultant opening can be filled on these 3 sides by extending the neighboring surfaces and intersecting them with the moved face which is also extended:



But not the last side:



Since that face is parallel to the one that was moved, those faces will never intersect each other no matter how much they are extended.



For those spots you would need use Extrude to punch them out instead.

It seems like I can probably detect this situation and automatically generate an Extrude, I'll give it a try.

- Michael