When working with some flat surfaces and having 1 such surface block selected: while moving them around in the editor, already placed surfaces are temporarily hidden. The glitch seems to be consistent, but dependent on the angle you're looking at the surface that gets hidden and the height you're on. Only the surface gets hidden. Not the border or the rest of the block.
The video shows the problem clearer than I could describe it.
The video shows the problem clearer than I could describe it.