Posted 2024-December-03, 21:31
Basic GIB needs the partnership to have more than some constant number of HCP in order to leap to slam, which isn't the case any time in this auction.
You'd think that it'd be trivial for Advanced GIB to simulate and see that it can bid 7♠ any time throughout the auction. But many rules tell advanced GIB to turn off simulations and make the book bid. And even if they don't, BBO "optimised" GIB so that it's only allowed to pick based on database rules that are 'close', for some rather incomprehensible definition of 'close'. (It used to try everything, so would have solved this easily.)
With 5-5 and 4 or less losers, 4♥ by North is forced and simulations disabled.
With at least one 3 card side suit, bidding the cheapest suit is forced for South, and simulations disabled.
Without support for clubs, bidding the cheapest suit is forced for North, and simulations disabled.
With North still not having shown HCP, no rules at all match for South, which causes it to pass without being able to think.
If South had responded 4♠ (or you reverse North's minors)... no rules would have matched for North, and it would also have passed without being able to think.
Yeah, GIB is totally broken on freak hands.