King Cole all in one 3504
Just did the legs to this pattern, casting on the 1 added stitch in the middle. I kept the +1 stitch and just following the knit/purl seed pattern because after the 15 rows of pattern, you have to start decreasing on each end.
If I were to start knitting this pattern again, I would not cast on this extra stitch. Even with the decreasing later on, it's only 1 stitch.
Must be a pattern glitch...tried looking up problems with this pattern and just found your inquiry here. I will make a note in my pattern not to add this cast on stitch for knitting this again in the future. It really throws you off, doesn't it ?