I turned the doubles threshold to 0 and blender still wants to merge my verts sometimes. I never had this problem before 2.7x.
I am creating shape keys for facial rig and I DO NOT want to change my topology.
I remember hitting that button a while back and not seeing what it did. I must have left it turned on.
Guess I have a bad habit of not reading the tool tips. You have saved me much future heartache