According to my Pfaff dealer you are not supposed to use the walking foot or the Pfaff even feed with any stitch that requires going backwards.
He said the the whole idea of the walking foot/even feed is to move the fabric forward evenly so doing anything the requires backing up is not good for the foot or the even feed mechanism. He said if you do it, the stitches are often distorted and you risk causin it to not work properly.
I have a Pffaf and it tells me on the LDC display when I choose a decorative stitch whenther I can can use the even feed or not.