Genetics of coat length

Does anyone know what happens if a medium coated dog (cavalier or cocker length) is crossed with a long coated dog (like shih tzu type hair)? I know generally medium+short=short, which would imply short is dominant-ish, as in the cute pup on the behaviour subforum atm – short haired cavalier/basset.

But in long-coated breeds like shih tzu or havanese there are sometimes medium haired versions which are recessive to the longhaired versions:

Short-haired havanese (nn Shavanese).

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