Minecraft Time/Mobs goes fast

Okay so, if you have been watching UHC you have already seen that they have some problems with the time/mobs speed

So today i was just trolling around with mobs at my local server, more and more mobs spawned ofc because of the 1.6.2 update, but later the server started too lag (Not FPS lag), just like it does in UHC Episode 5 and 6

Mobs freezing/Runs VERY fast and the day/night goes fast too

I do not have any proof but what you guys can try is too start a local/vanilla server, spawn some mobs, let the server stay on for a while

Video Link for the same case (UHC):
Speedy mobs/time
http://www.youtube.com/watch?v=trCSukJNLag&feature=player_detailpage&t=536
http://www.youtube.com/watch?v=trCSukJNLag&feature=player_detailpage&t=735
Freezing mobs
http://www.youtube.com/watch?v=KlQMXWeQwK4&feature=player_detailpage&t=594

Remember, i saw this at my Vanilla Local home server, so the server should not be lagging but it does