My partner and I messed up a big hand yesterday as follows. We play Stayman where the sequence 2C 2D 2NT shows 21-22 points balanced. Partner opens 2C I bid the relay 2D, and my left hand opp bids 2S. Partner bids 2NT, ignoring the intervention. I guess that she has ignored it. I have 11 points, a singleton spade and four card heart suit headed by AQ. If partner has 4 hearts I think 6H is on. So I bid 3C, Stayman, which my p takes to be a weak take-out and passes. She says "Can't be Stayman when opps have bid a major". Opinions please?
In the auction 2C (P) 2D (2S) // 2NT (P) ?? a cue bid of 3S would be a clarion call for a spade stopper or a heart (or some other) suit. If partner bids either 3NT or 4H you can go from there if you choose. If partner passes, get a your partner a new hearing aid. Cue bids are excellent general purpose forcing bids when you want to hear more from partner.
If my opponent opened a Weak 2S and I bid 2NT strong and balanced I play that 3C from partner is still Stayman so I don't see why you can't agree this sequence to be. There is quite a good case for simplicity by saying "system on" in such positions.