EDIT: Fixed the bug description, keeping the old description, just in case...

The entire bug seems to be about the game not following the division/multiply by 8 rule in the Nether/End placement when entering the said realms, which can lead to spawning inside blocks, or falling into the Void.

The bug can be reproduced in Creative mode and Survival mode in Multiplayer, Survival mode in Singleplayer.

ORIGINAL DESCRIPTION:

When creating a Nether Portal and entering it in a Multiplayer server, the player ends up in the Nether without a counterpart to the original portal, making it harder or impossible to return to the Overworld without dying.

The spawn seems to always be inside a ceiling, suffocating the player.