Given that it was me (the lady) underturning, we FINALLY fixed the problem. David and I both maintained a stiffer frame through the end of the turn so that his momentum could transfer to me, to finish up the turn. I think we must have practiced this 500x to finally nail it repeatedly. Normally, I can carry my own momentum through turns, but the man's crossing in front of me (with my stepping between his legs) as he does his spot turn, meant that I simply could not do it all on my own.