Heston Blumenthal's Perfect Potato Mash

DH tried to use this recipe (he actually used the video blog on Youtube) for the potato mash in Zander with Potato and Glasswort Mash. Unfortunately he managed to turn it into "DH's Perfectly Ruined Potato Mash" (the taste was nice, but the texture was very, very gluey), and we're still not entirely sure why.

He did two things differently: He didn't manage to keep the water at 72°C - it actually even came to a boil (whoops). And he started cooking too early, and therefore had to let the potatoes cool down after they were cooked the second time, and then reheated them with the butter; we suspect it was the latter that created the problem. Now if only Heston Blumenthal could also tell us why that happened... Oh, and DH also omitted the lime jelly, not that that would have made any change in the texture of the mash.

Edited the next day: We tried it again, managed to keep the temperature at roughly 72°C and didn't let the mash cool completely - and yet the mash turned gluey again. Not good. Next time we'll just do a plain old traditional mash again.