It looks to me like they left out a step - I know that when I've started a heel flap - I have to knit to the end of the heel and then purl back to the other side of the heel flap, then I begin the flap.
On your pattern it looks like you get to the heel marker, knit 15, turn and purl back 30, place remaining stitches(not heel stitches) on holder. Then begin your heel flap per the directions. Leave your heel marker and keep sliding it on each row of the heel flap, because you'll need to know later where the center back is.
Hopefully, my directions are clear. And if anyone sees a mistake in my directions or knows of an easier way - please post.
OTN - lacy sweater and just beginning another pair of socks - toe up
FO's: garterstitch scarf, dropped stitch cable fingerless mittens, socks for Christmas, and 6 baby hats, cabled toddler hat, hat for mom, MIL socks
My blog: http://knitquiltmom.blogspot.com/
I'm knitquiltmom on Ravelry... I'm slowly loading my projects. I also have several patterns that are being offered as free downloads.