Spawning rates reduced

For the past few days I've been getting ready to build an Endermen farm in the End on my server. I just got everything ready when the snapshot came out. When I tested the trap on a test world in the snapshot, the rates were substantially reduced, seeming to be only half the regular speed. I tried several times switching versions between 14w05b and 14w06b and 14w06b spawns mobs much slower. Thanks for reading.