Wow, never heard of that problem before.
I dont cut off my batting or backing until I have sewn the binding onto the front of the quilt. 1/4 inch onto the quilt top. I dont see how you can get a good mitre on the corner if you sew a larger seam.
I also machine sew in the ditch on the front to attach the back binding.
This is after I Elmer glue the binding to the back side No hand sewing for me.
Have never pined the binding to the front either and just stretch it a small bit as I sew it to the front of the quilt.
But I do square up my quilt top before I layer and quilt.