As I have not reported a suspect claim for a while, I have been on the look out for them. After a simple Jacoby and Blackwood sequence, South reached the excellent slam. He won the heart lead with the ace, drew a round of trumps and then said "I am wasting your time here. I will eliminate the hearts and play the ace and queen of diamonds. Whoever wins will have to lead a club or concede a ruff and discard."
"A nice line", remarked, East, the club's SB, "but it would have been even nicer if you had mentioned the missing trump. Now I agree that under Law 70C1, a trick cannot be lost to partner's spade by normal play, but it is still careless, but normal, to forget to draw the missing trump, especially as you have played exactly one round. My partner will exit with his second trump, and you will be deemed to misguess the queen of clubs." "One down, or do you want the TD to rubber-stamp it?".
How do you rule?