When I teleport out of world border /tp 29999990 100 0 and then try to fly out of the world, the game hangs up: graphics are freezed, controls does not work, but sound still works somehow (music will play later as usual).

About a minute later after hang up I sent SIGTERM to the game. Launcher show me the truth:

When I flew out of 30,000,000 game was stopped:

[22:46:02] [Server thread/INFO]: vovan_ve lost connection: TextComponent{text='Disconnected', siblings=[], style=Style{hasParent=false, color=null, bold=null, italic=null, underlined=null, obfuscated=null, clickEvent=null, hoverEvent=null, insertion=null}}
[22:46:02] [Server thread/INFO]: vovan_ve покинул игру
[22:46:02] [Server thread/INFO]: Stopping singleplayer server as player logged out
[22:46:02] [Server thread/INFO]: Stopping server
[22:46:02] [Server thread/INFO]: Saving players
[22:46:02] [Server thread/INFO]: Saving worlds
[22:46:02] [Server thread/INFO]: Saving chunks for level 'Новый мир1'/Overworld
[22:46:02] [Server thread/INFO]: Saving chunks for level 'Новый мир1'/Nether
[22:46:02] [Server thread/INFO]: Saving chunks for level 'Новый мир1'/The End
[22:47:02] [Client Shutdown Thread/INFO]: Stopping server

Note a delay in the end. It said, I exit immediately when flew out of 30,000,000.

Snapshots from 14w31a to 1.8-pre1 has same behavior, but previous snapshot 14w30c works more properly: it shows a message "Lost connection, Illegal position, [Back to main menu]".