Steps to reproduce the simpliest case:
- create a cube
- select one face and scale it to 0
The result looks like a pyramid, but obviously it's not, since we have 4 vertices (instead of 1) in the same place (if we, say, grab-X one, we get some mess, like in picture 4, not like in picture 5). How do I merge those into one? Or is there a better way to collapse a face into an edge with the same position?