Name tags display incorrectly when upgrading from 1.12.2

Mobs named using name tags display {"text":"Name"} instead of just Name when upgrading to 18w21b from 1.12.2.

For mobs named "Grumm" or "Dinnerbone", this means that they are no longer upside down, "_jeb" sheep are no longer rainbow coloured and "Toast" rabbits no longer show the correct skin.