In the new 14w02b version my old worlds from minecraft 1.7.4 are lagging and not loading correctly. EDIT: no longer just 1.7.4 worlds my 14w02c is skipping ticks about 50 it says.
EDIT: no longer just block lag it crashes when you join a 1.7.4 world
EDIT14w04a: when you click on a 1.7.4 world it will send you back to the title screen for about one min then let you into the world with immense block lag and skipping ticks
The error is mainly skipping ticks this only happens on worlds that are pre 1.8 snapshots any worlds created with the bug are fine

it does not crash anymore just all blocks and redstone don't update at all in these worlds and chunks take about 1-2 min to load
[14:55:26 INFO]: Client> [14:55:26] [Server thread/INFO]: snakecode01[local:E:b38a80e0] logged in with entity id 1484693 at (-668.8496383537884, 66.9680307906358, 1036.6570169378738)
[14:55:26 INFO]: Client> [14:55:26] [Server thread/INFO]: §esnakecode01§r joined the game
[14:55:26 INFO]: Client> [14:55:26] [Server thread/WARN]: Can't keep up! Did the system time change, or is the server overloaded? Running 15351ms behind, skipping 307 tick(s)
[14:55:43 INFO]: Client> [14:55:43] [Server thread/INFO]: Saving and pausing game...
[14:55:43 INFO]: Client> [14:55:43] [Server thread/INFO]: Saving chunks for level 'TestWorld'/Overworld
[14:55:43 INFO]: Client> [14:55:43] [Server thread/INFO]: Saving chunks for level 'TestWorld'/Nether
[14:55:43 INFO]: Client> [14:55:43] [Server thread/INFO]: Saving chunks for level 'TestWorld'/The End
[14:55:43 INFO]: Client> [14:55:43] [Server thread/WARN]: Can't keep up! Did the system time change, or is the server overloaded? Running 17193ms behind, skipping 343 tick(s)

the dev console gets to here an minecraft freezes for a while
[17:44:43 INFO]: Client> [17:44:43] [Server thread/INFO]: Saving and pausing game...
[17:44:43 INFO]: Client> [17:44:43] [Server thread/INFO]: Saving chunks for level 'Test'/Overworld
[17:44:43 INFO]: Client> [17:44:43] [Server thread/INFO]: Saving chunks for level 'Test'/Nether
[17:44:43 INFO]: Client> [17:44:43] [Server thread/INFO]: Saving chunks for level 'Test'/The End
[17:44:44 INFO]: Client> [17:44:44] [Server thread/INFO]: Stopping server
[17:44:44 INFO]: Client> [17:44:44] [Server thread/INFO]: Saving players
[17:44:44 INFO]: Client> [17:44:44] [Server thread/INFO]: Saving worlds
[17:44:44 INFO]: Client> [17:44:44] [Server thread/INFO]: Saving chunks for level 'Test'/Overworld
[17:44:44 INFO]: Client> [17:44:44] [Server thread/INFO]: Saving chunks for level 'Test'/Nether
[17:44:44 INFO]: Client> [17:44:44] [Server thread/INFO]: Saving chunks for level 'Test'/The End
[17:44:46 INFO]: Client> [17:44:46] [Server thread/INFO]: Starting integrated minecraft server version 14w04a
[17:44:46 INFO]: Client> [17:44:46] [Server thread/INFO]: Generating keypair
[17:44:46 INFO]: Client> [17:44:46] [Server thread/INFO]: Preparing start region for level 0
then loads a broken world with this in the console
[17:45:06 INFO]: Client> [17:45:06] [Server thread/INFO]: snakecode01[local:E:2ba7eec1] logged in with entity id 56325 at (-666.3116477960418, 56.0, 962.6566203104643)
[17:45:06 INFO]: Client> [17:45:06] [Server thread/INFO]: §esnakecode01§r joined the game
[17:45:06 INFO]: Client> [17:45:06] [Server thread/INFO]: Changing view distance to 16, from 10
[17:45:07 INFO]: Client> [17:45:07] [Server thread/WARN]: Can't keep up! Did the system time change, or is the server overloaded? Running 19828ms behind, skipping 396 tick(s)
[17:45:27 INFO]: Client> [17:45:27] [Server thread/INFO]: Saving and pausing game...
[17:45:27 INFO]: Client> [17:45:27] [Server thread/INFO]: Saving chunks for level 'TestWorld'/Overworld
[17:45:27 INFO]: Client> [17:45:27] [Server thread/INFO]: Saving chunks for level 'TestWorld'/Nether
[17:45:27 INFO]: Client> [17:45:27] [Server thread/INFO]: Saving chunks for level 'TestWorld'/The End
[17:45:27 INFO]: Client> [17:45:27] [Server thread/WARN]: Can't keep up! Did the system time change, or is the server overloaded? Running 20215ms behind, skipping 404 tick(s)

Note when 1.7.4 world loads redstone clocks do not seem to work nor does most redstone check image below to see redstone not working properly the clock does not update no matter what is done.