Ask Robin - Mechanical Error
Another interesting and informative Ask Robin section in the latest English Bridge Magazine.
I hope you don't mind me suggesting that the final Ask Robin answer could've been enhanced by offering a bit more guidance on the questions TDs should ask. For those with very slow postal delivery, the scenario is: 2NT (20-22) passed out. Declarer's partner had ten points, claimed their pass was mechanical error and that they mean to bid 3NT. TD agreed. Robin advises TDs to be sceptical of mechanical error explanations.
In this case I think the key questions are did declarer use the Stop! card and (much more importantly) did partner announce "20-22". If it was announced then you can rule out partner thinking it was 1NT and mechanical error seems more likely.
I can imagine a ten pointer would consider 4NT quantitative and then decide against it. They think "let's not go any further and just settle in 3NT" and, getting ahead of themselves, they accidentally pass. If they offered this explanation, is this a mechanical error or a loss of concentration?