Issues with GIB showing preference of my suits

[terpdrew]

I have noticed this a few times now over the past week or so that I've been playing in robot tournaments. When I bid multiple suits, asking GIB to show a preference, they haven't gone with the suit we have the best fit in - which doesn't make any sense to me. A few days ago, it was something as simple as 1S(me)-1NT(GIB)-2D(me) and he put me back in spades despite having 4 diamonds and only 2 spades. The one today was a bit more convoluted, but still didn't make sense to me. Hopefully, I've attached it here...

 

http://tinyurl.com/yyxdszra

 

When I looked at the explanation under my bidding, GIB has me shown correctly as 5-0-4-4, but then he shows preference for diamonds (despite having 3D and 4C?!?), so that we go down in 5D as opposed to making 5C. I don't understand this at all.

[BillPatch]

GIB 2/1 regularly gives false preference back to the first suit in certain auctions. Your first sequence is of the form 1 of major-forcing, semi-forcing, or passed hand 1 NT response-2 of minor opener's rebid. On this sequence all forms of 2/1 I have read use the false preference back to the major with a doubleton with a minimum response. This allows opener with an intermediate opener with a 6 card major which will not play well opposite a singleton offer the choice of the minor if there is no 8 card major fit.

 

In the diagramed hand GIB correctly gave a false preference according to its system. The alert of the 4 ♣ bid was misleading. While only a 5=0=4=4 technically meets the criteria for the bid, GIB will bid a 5=0=5=3 the same way up to that point. As the 5-5 hand does not meet any defined criteria it simulates the results of bids that that have criteria with a one card different and simulates those against a pass. On the next round the defined criteria for the 4 ♦ bid checks back for a 5-3 fit. If you check back on the alert for your 5 ♦ bid it has a 5 card ♦ suit requirement. The correct final bid according to this treatment for your hand was 5 ♣. With a true preference for ♦ GIB would correct the contract to that suit instead of passing.