Vampyr, on 2019-August-05, 14:57, said:
No, normally with a stopper you would bid NT to protect the stopper.
3♠ would normally say that you don't have diamonds stopped as you have shown a heart stop with 1NT, and the concept of protecting the stopper is ridiculous when you have already bid 1NT yourself. However it does not matter what it says; for you to disallow it you would have to say that it is demonstrably suggested over other calls by the UI. I think that bidding on IS suggested over Pass which is an LA, and that is why I would disallow 3♠, and that is because a slow 2♠ normally suggests that you would not mind hearing from partner again. I think if you poll Easts with the methods that you have no CC, and think that 1S denies spades, then many Easts would now pass an in-tempo 2♠.