Never pass a mystery bid.
If 5♦ was intended as an alternate contract (as it seems), S has a clear preference back to 5♥
If 5♦ was intended as lead-directing if opps land in 5♠, S can never gain by relying upon N to correct back ...
Yes to Andy and Hanoi, I hope that all of the above actions are considered ethical. My main point of curiosity is whether players might adjust "mid-flight" as it were to account for the potential impact of their BIT. (edited to fix a spelling error)
Seems to me this would sanction the use of a deliberately-insufficient-then-withdrawn call as a lead *excluding* call.
1♦ 2♥ P 4♥
1♦ ==> "don't lead diamonds"
- the insufficient bidder is willing to play there if need be but would rather withdraw the call
- declarer ...
@Michael, thank you for your explanation here. I didn't quite savvy this argument earlier. The higher degree of uncertainty in opener's rebid -- as indicated by the BIT -- could demonstrably suggest the value of a more flexible call rather than a more unilateral one. Got it.
Changing my vote...