Misbid?
Opener bids a Precision 1D, partner responds 2NT, described in their system as showing precisely 11-12 HCP with no 4 card major.
Opener rebids 3NT.
Partner then bids 4NT and Opener raises to 6 NT.
When asked Opener says that his partner has obviously forgotten their system and has a bigger hand, so having a maximum opening hand he raised to 6.
Should this be allowed?
Comments
Assuming there were no alerts and no explanations (of the NT bids) during the auction then ...
Opener has no unauthorised information it appears he can bid as he likes.
If responder thought 2NT was balanced and forcing, then he has unauthorised information from the lack of alert. But responder may be so strong that Pass is not a logical alternative, in which case all routes probably lead to 6NT.
Other than the "did 4NT use UI?" argument, the only other argument for an infraction that I can see here is that the 4NT bid is a psychic control (because it indicates that responder made a bid that can't possibly fit their hand).
I think that only happens if this situation comes up often enough to have an established meaning about what 4NT means, though. A psychic control surely has to be an actual agreement, rather than something that was improvised on the spur of the moment. (And if 2NT was a misbid and the lack of alert didn't clue responder in to something being wrong, 4NT couldn't have been a psychic control because responder wouldn't realise that they'd made a bid that didn't match the description.)