No facts to back this up this is purely a guess on my part. I know I am going to hear a lot of shit about this post, but this is what my gut tells me. A hand full of people are pushing the market up slowly to make it more believable.
I too get the feeling that there are somewhat larger players also pushing the market up, not just down. Since currently the bulls are in the majority here, we're all paying way more attention to the ask walls. But there are constantly these 1000 sized support walls, below, which are moved up slowly. Whenever there is a market dip action, they get pulled away very quickly, just to reappear below once the ripples have ceased.
Now, this could be a group of people trying to push the market up, thereby competing with a group of bears.
But it could as well be someone trying to take some constant profit from the bounces. Placing walls above and below can be a comparatively risk-less short-time strategy, when not wanting to go either side exclusively. Just need to assure you pull the walls quickly whenever any kind of stronger market action arises. You could even plant the walls just as guide and place your real offers of smaller size in between.
(ok, there remains the risk that someone similarly capable just swallows one of your walls all at once)
ones here, but it seems to me a lot of data could be gleaned from placing a solid wall and watching the reaction. 
