Rapid memory Cycle

I started a superflat world in 13w39b and started to build various things. I placed a bed and went to bed at night to set my spawn point. After that I started to notice the used memory started to cycle faster and faster. It does NOT affect mobs, blocks or sky or the fps.

here is a video link showing it along with a closeup on YouTube. (fps in video is low due to bandicam, not bug)

http://youtu.be/-0uK_o-WFGU