I have a mob grinder that worked pretty consistently in 1.2 but now it seems very sporadic with mobs. Mobs seem to come in a big group and then suddenly not spawn for a while. The spawning space is about 36x36, 2 high and a couple extra levels a bit smaller than that about 36x24 or so. The collection point is below the spawning spaces, relatively close to the center of all these spawning spaces.
Sporadic is right. I've seen this issue since the latest update too. My grinder gets waves of mobs instead of the steady stream I used to get. Some others have seen this change too in this thread: http://www.minecraftforum.net/viewtopic.php?f=1020&t=204816
I've been having the same issues too. Meh sheep seem to come only in groups, then they'd stop spawning :sad.gif: On the other hand XD I get HUGE groups of creepers and I get to make lotsa tnt XD
is mob spawnining different for 1.3?