So I've paid closer attention to what I've done here.
I knitted row 30 and all the stitches seem to have worked out. It is when I get to row 31 that I have a problem.
Row 31 begins with k14, I only have 13 stitches before I get to the bound off stitches. If I were to knit 13 and then do my cast on, I would end up with an extra stitch by the end of the row.