[barmar]

It happened again. I stayed out of a NT game that should go down, and the bots let all the declarers who bid it make, because they didn't continue the suit when the opening lead was in their 5-card suit and declarer ducked. Here's a typical one:

http://tinyurl.com/27oe9xv

I was in the ♦ slam, which I think is better than 50%, going down 1 because I'm not a rabbi. On a ♥ lead, 3NT should also go down when declarer fails to drop the stiff ♣K, as long as East continues when declarer ducks. But instead, it switches to ♠. This happened at 3 of the 4 tables where 3NT was bid (the 4th had a very different auction, and West decided to make a passive ♠ lead).

I think this is another fault of its use of double dummy analysis. GIB presumably figured out that that if declarer only has ♥A, it must have ♣QJ for its opening bid. And since it expects declarer to play double dummy, it knows its K will be dropped.