The single stitch is overrunning. This also affects how the needle is pulled up by the "auto pull-up" feature and how the needle is positioned after stopping the sewing both in regulated and constant speed mode. You need to move the needle up position (Page 7.) backwards. The proper take-up lever position on Gammill machines is at the top edge of the head. On APQS machines you need to set the "up" position where the needle is at its highest position. Please note that changing the take-up lever up position affects the needle down position also, so you need to check it too. The proper needle down position is when the needle is about 1/4" BEFORE its lowest position. Note that on Gammill machines at this needle position the take up lever is aligned with the top edge of the head, on its way down.