The bug
Prior to 19w37a, when using a horse, donkey, mule, llama or trader llama spawn egg on a block (while not looking at an adult animal), occasionally a baby horse, donkey, mule, llama or trader llama would be spawned instead of an adult animal (see MC-135098). That does no longer happen.
Linked issues
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Comments 2
Confirmed in 19w38a and 19w38b.
migrated
Personally I feel like it would be better if only adults spawned under these conditions. Spawn eggs are meant to be a convenient Creative mode tool for spawning specific mobs and having only adults spawn would be more consistent with other eggs, as babies may be undesirable.