Thijs Lacquet

@Anthony Martin That has nothing to do with the bug reported here. Your log is showing that the server is trying to spawn mobs in CORRUPT chunks. The bug reported here has to do with the way the mobs are divided across the server.

Galaxy, this bug still affects current Minecraft versions, like 1.7.4.

Alexander, the zipcrowd guys made a server side mod which does exactly what the vanilla server should do. The video is linked in the discription.

Yes, but they should not be completely deleted, after the crash they don't exist anymore in the worlddata. And that happens every time, and the worlddata is just fine every time.

For instance, it would be better to read the files one time when the server is started, saving the data on the RAM, and writing it back in the map data every minute.
It would cause a lagg spike if you would write all the playerdata files at the same time, but you could also write every playerdata file seperetely with a little delay between that.
This would minimise the change of file loss during a system crash, and would not cause all the files to be simply deleted.

Another solution would be to sort of back up the playerdatafiles every hour, so a systemcrash would cause just a small rollback with the playerfiles.

So anoying, you cant let Minecraft use half of your screen, while switching between Minecraft and a youtube tutorial on the other half

Or another possible abuse:
Have 200 zombie's with 1 peace of cobble in their hand (so they wont despawn), in a small box at the border of the spawn chunks. Have a system which transport them all (with pistons or water) 1 or 2 blocks to the side. So they will leave the spawnchunks.
With this mechanism, you could completely turn on and off mob spawning with redstone in vanilla survival.

Neospectator, This could also give problems when players are AFK, because all the mobs will spawn in just the area of the AFK-ing player, and when other players log in, then they won't have mobs in their area.

The mob cap is similar to this both in SSP and in SMP when the people are close to each other, it completely works as how its suspected to be, but it starts giving problems when someone is AFK-ing, or when multiple people are in different area's on a server, mojang just didn't consider these kind of situations. And a lot of people will agree with me, that letting one player AFK should not remove the mobs for the other players. Mojang didn't intend that it is possible to use this trick.

Also, mojang added hoppers in 1.5, its ability to pickup items is mostly used by mob farms, if Mojang wanted to ban those farms, they could just remove the possibility for hoppers to pickup items.

The fact that there are less mobs, when there are more players on a server is buggy. Something like a mobcap, cant be universal, mobfarms shouldn't be affected by another player over 1000 blocks away, but that's how it is right know. So this is not a feature, but a bug.