Steps to Reproduce:

1) Summon Ghast
2) Push through Nether Portal
3) Follow through same portal.

Also works if you have one player in the nether, and one in the overworld waiting.

Behavior:
Ghasts pushed through portal appear on other side for a fraction of a second before vanishing.

Occasionally where they vanished, blocks cannot be placed. Restarting the server resolves this block placement issue,