Mobs will not spawn during the night, only spawn when near a spawner.

Ever since the update to 1.6.2 my online server will NOT spawn mobs above on land, in the nether, in the end, or in caves. only when i go near mob spawners they spawn, i have gone throug hthe server settings, tried every difficulty and even thrown spawn eggs, they DO NOT spawn themselves during the night. can somone please help?