Mob spawning behaviour affected by render distance.

Lately, since I updated my singleplayer world to the snapshot 14w11b I've been noticing that mob spawning rates are completely affected by render distance. As my computer si not very good, I usually play at 4/6 chuncks and I realised almost no mobs were spawning in my world. I don't know if it is a bug or it is actually intended. Also, the rates of my enderman farm have hardly decreased.