When you try to spawn a mob with a spawn egg, the mob disappears right after you spawn it.

Put the summary of the bug you're having here

What I expected to happen was that it would stay after it spawned.
What actually happened was that it disappeared after spawning.
1. Grab a spawn egg from Creative Mode.
2. Go to Survival Mode
3. Spawn the mob, it should disappear right as it appears.
*Note, it only works on ANIMALS, not Villagers.