SpigotMC/Spigot-Server — pull request #65 by Blackberry0Pie (2013-08-29 21:50:57+00:00)
Title: Update SpawnerCreature.java

SMP mob cap doesn't scale to the number of people online(this is a vanilla MC problem).
Solution: multiply the mob cap by the number of players to scale the mob cap to the number of players online.