Has anyone done these socks in medium? I'm at the directions for Working the Heel Flaps on page 70 and it says to use 33 sts. If I do this and do repeat of Slip1, K1, I end up with the last stitch on row 1 slipped. Then row 2 slips the first stitch. That means that this stitch never gets knit or purl which doesn't seem right. It wasn't listed on the book's errata.

the pattern may be missing a set of directions. The heel flap should be on an odd set of stitches, which it is and the piece of direction you may be missing is that the first and last stitch in the row is always knit. It should read k1, (sl, k1) to end of row. Try it like that and see if it makes sense.

Always knit the last stitch and slip the first one. So for your row of Slip 1, k1, you should just end with k2. Then slip the frst stitch of the next row.

Well it seems you got the information needed---good luck on turning your heel once the flap is done

Sounds like a plan - just add a K2 at the end instead of slipping. Many thanks for everyone's suggestions.