Right-clicking a mob with a mob egg spawns a baby mob

Put the summary of the bug you're having here

What I expected to happen was that the egg would spawn a single pig, and nothing else.

What actually happened was that the pig spawned with children and then i spawned another one and they started multiplying extremely fast, without breeding them, and without heart animations.
Describe what happened here

Steps to Reproduce:
1. Make a square room with a wooden door.
2. Spawn a pig or two.
3. The bug starts.