[pescetom]

A real world claim at a lower level, simple but with some wrinkles.

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West (intermediate) is Declarer in 4♠X. North (almost intermediate) leads ♦J to the K of South, who continues diamonds ruffed by North.
North then plays ♣K which holds and mistakenly continues with the Q, ruffed by West.
West pulls trumps from the top (discovering the unlucky split), leaving North in Hand.

North contemplates the dummy now down to ♥AT9 ♦AT for some time, uncertain whether to lead a heart or a club.
West lays down his hand containing ♠63 ♥J7 ♦Q and says "it's all mine: the trumps, the hearts Ace and the diamonds are all winners".
North frowns and says "No, play on" and immediately tables a heart. West refuses to play on and calls you, the Director.

How do you proceed and what are your concerns?