The player character is sometimes falling a small distance after entering nether or overworld through the portal (I believe it might be about 1 or less than 1 block). Sometimes you can even hear a falling sound effect, but so far it hasn't harmed the player character.
I tested it on portals with a different y coordinate (different altitude). I only used the smallest portals possible (the ones with 4x5 obsidian frame). I didn't test it on a pair of portals with the same y coordinate.
Steps to reproduce:
1. Create a pair of portals (matching x, z coordinate, different y coordinate)
2. Go through the portal
3. When you enter the other dimension, you fall a bit (you can see it with debug information turned on).
Comments 3
I guess that's the reason. It certainly sounds plausible - it happens often and regardless of the number of the chunks rendered (I checked it with 2 chunks rendered as well and it's a minimal setting).
It affects previous snapshot (13w49a) and 1.7.2 as well.
Thank you for the explanation - the falling sound effect at first sounded like a sound system glitch but it appears to be rather related to the chunk loading.
I think this is caused by the minecraft chunk loading. The chunks unload when you go through the portal, so when you come back, you get into unloaded chunks, what causes you to fall. The blocks just haven't loaded yet. As soon as the chunks are loaded, it will update, and you will be "teleported" up.