This was a very interesting hand, in that something happened on this hand that I have never seen before.
This was Board 6 in a 12 board match in our local round robin team event played earlier tonight. My partner and I were definitely having the better of this match, and I estimated that we were up by about 30 IMPs over the first 5 boards. This board started a reversal of fortune in the most bizarre way.
I was North. I led the ♥J against 4♠x. My partner won the Ace and returned the ♦7 to the 6, J and A. Declarer led the ♠K off dummy won by my partner's A. Partner led the ♦5, declarer following with the 9 and my Q winning. Not seeing anything unusual, I cashed the ♦K, partner pitching a club AND DECLARER RUFFING! It was at this point that dummy noticed the ♦8 stuck under the ♦10. Declarer played a spade to dummy's Q, both of us following, and then the ♦10 off dummy. My partner ruffed with his last trump. Declarer overruffed and then ran his KQ10 and 9 of hearts, pitching all 4 clubs off dummy (his diamond on dummy was also good, so he could have pitched his only club). MAKING 10 TRICKS!
Sure, I could have noticed that dummy only had 12 cards. But I didn't. Neither did declarer, my partner, or the dummy. NO ONE NOTICED.
Is there any exception to the rule that all of the players are responsible for the dummy? This result feels wrong to me. Obviously if I had seen the 5th diamond in dummy I would have cashed my ♣A for down one. So instead of a 3 IMP win against 4♠ undoubled down one at the other table, we lost 13 IMPs. This cost a number of VPs, as we only won the match by 10 IMPs.
(Yes, it is bizarre that East didn't double 4♣, but that is not the point of this post)
EDIT: Auction and play fixed. Sorry for the inaccuracies.