Unwanted hard edges with subdivision modifier This happens everytime I merge some vertices and then apply the subdivision modifier. I've tried removing double vertices and even if I delete the edge that seems to be causing the problem this happens: 



It just transfers to the next edge. Does someone know why it looks like it sticks to the original mesh? Any ideas on how to fix it are welcomed!
Check if you have an internal quad, which is made with those edges. If there's a quad, delete it.

Also check the Mean Crease of those edges (1 means hard edge, 0 means soft edge):