I was trying to move my wolves to my base using the nether. When I pushed them through the portal and went through myself, they had vanished. I logged into a test world and experimented a couple of times. It happened with all mobs I tried.

What I expected to happen was...:
When I pushed the wolves through the portal, they should have appeared in the nether.

What actually happened was...:
None of the mobs that had been pushed through appeared either in the nether, or in the overworld (when pushed back).

Steps to Reproduce:
1. Spawn or summon a mob next to a nether portal. (Skeletons, cows and tamed wolves were tested.)
2. Push spawned/summoned mobs into the nether portal.
3. Go through the nether portal and look around for the mobs.