that the cubes shatter into fine pieces when breaking out

Two of the four trays work as expected. Water freezes into ice, and the cubes pop out with a gentle twist. The other two are another story, however. On these two trays the ice sticks firmly to the plastic, and it takes more energy to break them free. The ice is adhered so well to the plastic, that the cubes shatter into fine pieces when breaking out, making them virtually useless. Very strange. We thought this would go away with subsequent washings, but it seems to be a property of the plastic itself. How do you mess up an ice tray?

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