....or rabbit ears
These are usually caused when the seam allowance waivers - less or more than the correct width - as it nears the end of the side. There is a tendency to lose control of the machine about 1/2" or so before getting to the end. If you rip out the binding if you see this happen, usually you see that it is the seam allowance.
Also, when you fold the binding down to make the mitre and sew on the next side....these folds must be exact on their proper angle in order to have a good mitre. Sharon Shamble, in her video, emphasizes that the fold at this point, which is in the verticle position or along the side of the next side - that the top fold should be very slightly in from the edge. I would call this the fuzz or threads of the layered quilt. Often the diagonal fold below the top may not be exactly lined up with the top fold. Another indication that a problem may occur is when you fold the binding to the back at the end of the row.......the fold that extends beyond the next side of the quilt, should be straight and exact and not at an angle.