It looks like the walking foot is a long straight foot. It looks like it happens before and after the seem when the foot is at an angle. I thought I had seen a video or web page describing what happens when you come up to a seam. I can't find it now. It is generally regarding heavy denim seams, but I wonder if that could also happen with a walking foot. Some have used cardboard, folded fabric or a designated tool to raise the back of the foot when coming to a seam. Once the foot is on top, you need to place it in front of the needle but not stitch into the whatever you are using. You need to keep the foot parallel to the bed until it is past the seam.
Janey - Neat people never make the exciting discoveries I do.