Cutmull-Clark subdivision seems bugged in very simple case

Hi, I was trying to model a dimple in a couch upholstery and I created the following simple shape representing 1/4 of what I want, using 7 vertices:


As you can see, applying subdivision breaks. The center vertex is pulled down towards the lower one of there is an edge there. I need that edge so that I can chamfer a fold in the fabric. The screenshot isn’t obvious so I’ve attached my blender file. Thanks for any help you can give me to correct this issue.

Couch.blend (442 KB)

Stay clear of triangles on a non planar surface when using the subsurf modifier


It’s not the subsurf that is bugged, it’s in fact your mesh that has a very bad problem, there are 3 quads and a “floating” edge that isn’t a part of any faces :
http://i.imgur.com/7pfeiO8.jpg
And that’s why the subsurf does something bad.

My guess is that you tried to cut an edge inside of the original quad by selecting 2 vertices of it and pressing F instead of J.
If you press F with 2 vertices selected it will create a “floating” edge that is part of no face, unlike pressing J that create the edge inside of the face

So select only that bad edge and press X -> Edge to delete it
Then reselect the 2 vertices and press J, you will then see that the subsurf does not create any hole.