Using spawn eggs on slimes/magma cubes does not spawn the smallest type of slime/magma cube

Very likely WAI, but I've seen other people complaining about this, so I figured I'd post it here just to be sure. Relates to MC-2871 and MC-165524.

When using a spawn egg on a slime, one may expect a tiny slime to be spawned as a result, analogously to spawn egg mechanics spawning baby mobs when used on adult mobs. However this is not the case and nothing is spawned at all.