I've never had any issues and love mine. The ruler only works one way. Make sure that the seam allowance is in the ditch. and the edge of the ditch is firmly against the sewn seam. I also usually use mine with a rotating cutting mat. If you don't have one, then just use a small mat and turn the mat as you cut. Finally, don't use a dull blade. The duller the blade, the more pressure you need to put on the blade and the tendency is to also push harder against whatever ruler you are using increasing the possibility of slipping.