[Bbradley62]

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Despite South's break in the system, it seems to me that North should bid 2♥ over 2♦.

[dicklont]

So it seems, but your pass on a forcing call made North guess. And it looks like he guessed your hearts were not for real.

[iandayre]

I suppose that is true. A pass of a "forcing" 1NT response should be defined as a good 11 to bad 13, exactly 5 of the major, and no side 4 card suit or singleton. If the programmers do not choose to have GIB pass that sort of hand itself, at least it should know what to expect when partner does. I routinely pass such hands and overall my results have been quite good.

[1eyedjack]

It goes back to a more fundamental question of which this hand just scratches the surface: when an unseen hand makes a systemically impossible call, but one with which GIB is required to cope in a live auction, what assumptions should it be making?

By far the majority of such cases will be passing a forcing bid. Not all, though (ie bidding beyond 2S in response to Stayman).

Dealing with the passers should be the easiest case, I feel: Minimum hand and tolerance for the trump suit (if not in NT), but otherwise best "fit" with previous descriptions. That would have told North what to do on this OP hand.

This problem is rather different from the situation where GIB can tell that someone is telling fibs but not sure who (the more than 40 points in the deck syndrome). In that case it should probably trust partner and then "best fit" the oppo hands in context.