Whenever you get on a horse or mine cart chunks cease to load. When you get near the edge of the loaded chunks the game has a possibility of freezing the game.

log for first screenshot:
[23:54:54] [Client thread/INFO]: Setting user: jex0
[23:54:54] [Client thread/INFO]: (Session ID is token:478e1144838f4bf589b013b10087df73:34223e7ade27442a951b25d2f2e2aae0)
[23:54:55] [Client thread/INFO]: LWJGL Version: 2.9.4
[23:54:56] [Client thread/INFO]: Reloading ResourceManager: Default
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:block.brewing_stand.brew
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:block.chorus_flower.death
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:block.chorus_flower.grow
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:enchant.thorns.hit
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:entity.guardian.thorns
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:entity.horse.eat
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:entity.player.attack.crit
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:entity.player.attack.knockback
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:entity.player.attack.parry
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:entity.player.attack.strong
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:entity.player.attack.sweep
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:entity.player.attack.weak
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:entity.rabbit.attack
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:entity.shield.block
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:entity.shulker.ambient
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:entity.shulker.close
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:entity.shulker.death
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:entity.shulker.open
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:entity.shulker_bullet.hit
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:entity.shulker_bullet.hurt
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:entity.witch.ambient
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:entity.witch.death
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:entity.witch.drink
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:entity.witch.hurt
[23:54:56] [Client thread/WARN]: Missing sound for event: minecraft:entity.witch.throw
[23:54:56] [Sound Library Loader/INFO]: Starting up SoundSystem...
[23:54:56] [Thread-5/INFO]: Initializing LWJGL OpenAL
[23:54:56] [Thread-5/INFO]: (The LWJGL binding of OpenAL. For more information, see http://www.lwjgl.org)
[23:54:57] [Thread-5/INFO]: OpenAL initialized.
[23:54:57] [Sound Library Loader/INFO]: Sound engine started
[23:54:58] [Client thread/INFO]: Created: 1024x512 textures-atlas
[23:54:58] [Client thread/ERROR]: Realms module missing
[23:55:02] [Server thread/INFO]: Starting integrated minecraft server version 15w45a
[23:55:02] [Server thread/INFO]: Generating keypair
[23:55:03] [Server thread/INFO]: Preparing start region for level 0
[23:55:03] [Server thread/INFO]: Changing view distance to 6, from 10
[23:55:04] [Server thread/INFO]: jex0[local:E:a2332793] logged in with entity id 14 at (672.0060408295483, 1.8500000178813933, -105.69868991184279)
[23:55:04] [Server thread/INFO]: jex0 joined the game
[23:55:05] [Server thread/INFO]: Saving and pausing game...
[23:55:05] [Server thread/INFO]: Saving chunks for level 'redstone'/Overworld
[23:55:05] [Server thread/INFO]: Saving chunks for level 'redstone'/Nether
[23:55:05] [Server thread/INFO]: Saving chunks for level 'redstone'/The End
[23:55:31] [Client thread/INFO]: [CHAT] Saved screenshot as 2015-11-07_23.55.30.png
[23:55:32] [Client thread/INFO]: [CHAT] Saved screenshot as 2015-11-07_23.55.32.png
[23:55:33] [Server thread/INFO]: Saving and pausing game...
[23:55:33] [Server thread/INFO]: Saving chunks for level 'redstone'/Overworld
[23:55:33] [Server thread/INFO]: Saving chunks for level 'redstone'/Nether
[23:55:33] [Server thread/INFO]: Saving chunks for level 'redstone'/The End
[23:55:41] [Server thread/INFO]: Saving and pausing game...
[23:55:41] [Server thread/INFO]: Saving chunks for level 'redstone'/Overworld
[23:55:41] [Server thread/INFO]: Saving chunks for level 'redstone'/Nether
[23:55:41] [Server thread/INFO]: Saving chunks for level 'redstone'/The End
[23:55:44] [Client thread/INFO]: Stopping!
[23:55:44] [Client thread/INFO]: SoundSystem shutting down...
[23:55:44] [Server thread/INFO]: Stopping server
[23:55:44] [Server thread/INFO]: Saving players
[23:55:44] [Server thread/INFO]: Saving worlds
[23:55:44] [Server thread/INFO]: Saving chunks for level 'redstone'/Overworld
[23:55:44] [Server thread/INFO]: Saving chunks for level 'redstone'/Nether
[23:55:44] [Server thread/INFO]: Saving chunks for level 'redstone'/The End
[23:55:44] [Client thread/WARN]: Author: Paul Lamb, www.paulscode.com