Vampyr, on 2017-March-12, 03:37, said:
IMO, You must alert when you open 1N and partner replies 2♣ (say) that could be natural but which you never raise, because, systemically, it might instead show a shortage with other suit(s).
At favourable vulnerability, partner might pseudo-psych opponents out of their best game or slam.
If you're vulnerable, opponents safest option might be to pass the response, hoping that your partner will be left struggling in what might be a 2-2 fit or worse.
If you fail to alert, however, opponents, duped into assuming your bid to be natural, might be tempted to double, allowing you to escape to a 4-4 or better fit.
An opponent, with a strong holding in your partner's putative suit, can hardly ask to protect himself, without imparting blatant UI.
In practice, failure to alert is the norm; In general, directors seem unconcerned about disclosure.
Please assume EBU regulations but I hope that failure to alert would be an infraction, at least in theory, under any regulations.