[MC-70205] New Worlds take minutes to open

When I create a new world nothing generates and I slowly drift downwards. Eventually the world appears and I get teleported to ground level.

If I quit the world before it was finished it takes a long time to close but after re-opening the world is there but mobs are not moving and I do not take fall damage.

This happend first in the 1.8 snapshots and does not affect my existing worlds when I open them with a pre-release.

[04:14:35] [Client thread/INFO]: Setting user: sdf1981cgn
[04:14:35] [Client thread/INFO]: (Session ID is token:30c3f2dcdd9f4910a940f9fd47134916:6bfd23864d57491e88abbd7c3944d744)
[04:14:36] [Client thread/INFO]: LWJGL Version: 2.9.2
[04:14:37] [Client thread/INFO]: Reloading ResourceManager: Default
[04:14:38] [Sound Library Loader/INFO]: Starting up SoundSystem...
[04:14:38] [Client thread/WARN]: File minecraft:sounds/mob/ghast/fireball.ogg does not exist, cannot add it to event minecraft:item.fireCharge.use
[04:14:38] [Thread-7/INFO]: Initializing LWJGL OpenAL
[04:14:38] [Thread-7/INFO]: (The LWJGL binding of OpenAL.  For more information, see http://www.lwjgl.org)
[04:14:38] [Thread-7/INFO]: OpenAL initialized.
[04:14:38] [Sound Library Loader/INFO]: Sound engine started
[04:14:40] [Client thread/INFO]: Created: 512x512 textures-atlas
[04:15:10] [Server thread/INFO]: Starting integrated minecraft server version 1.8-pre3
[04:15:10] [Server thread/INFO]: Generating keypair
[04:15:11] [Server thread/INFO]: Converting map!
[04:15:11] [Server thread/INFO]: Scanning folders...
[04:15:11] [Server thread/INFO]: Total conversion count is 0
[04:15:11] [Server thread/INFO]: Preparing start region for level 0
[04:15:12] [Server thread/INFO]: Preparing spawn area: 10%
[04:15:13] [Server thread/INFO]: Preparing spawn area: 23%
[04:15:14] [Server thread/INFO]: Preparing spawn area: 39%
[04:15:15] [Server thread/INFO]: Preparing spawn area: 57%
[04:15:16] [Server thread/INFO]: Preparing spawn area: 75%
[04:15:17] [Server thread/INFO]: Preparing spawn area: 92%
[04:15:17] [Server thread/INFO]: Changing view distance to 32, from 10
[04:15:18] [Server thread/INFO]: sdf1981cgn[local:E:4ee62227] logged in with entity id 183 at (253.5, 68.0, 251.5)
[04:15:18] [Server thread/INFO]: sdf1981cgn joined the game
[04:15:52] [Server thread/WARN]: Can't keep up! Did the system time change, or is the server overloaded? Running 34044ms behind, skipping 680 tick(s)
[04:15:59] [Client thread/INFO]: [CHAT] Saved screenshot as 2014-09-01_04.15.58.png
[04:16:18] [Server thread/INFO]: Saving and pausing game...
[04:16:18] [Server thread/INFO]: Saving chunks for level 'New World'/Overworld
[04:18:15] [Server thread/INFO]: Saving chunks for level 'New World'/Nether
[04:18:15] [Server thread/INFO]: Saving chunks for level 'New World'/The End
[04:18:16] [Server thread/INFO]: Stopping server
[04:18:16] [Server thread/INFO]: Saving players
[04:18:16] [Server thread/INFO]: Saving worlds
[04:18:16] [Server thread/INFO]: Saving chunks for level 'New World'/Overworld
[04:18:16] [Server thread/INFO]: Saving chunks for level 'New World'/Nether
[04:18:16] [Server thread/INFO]: Saving chunks for level 'New World'/The End