I'm trying to mirror an arch and then subdivide to get a smooth look but vertices that should be merged in the process do not behave as I would assume. I cannot subdivide and moreover, shading gets distorted.
Here's a youtube video: https://www.youtube.com/watch?v=w3lguvtfWr0
How can I apply this mirror modifier so it works normal?
PS:blender 2.78a
