It looks like one is able to create walls in Bitcoin Central without having the necessary funds to do it.
For example, if I have 20 BTC in my account, I am able to place as many sell orders at 9.5€/BTC (let's say 50 of them). They will appear as a 1000 BTC wall at 9.5€/BTC in the order book and in the graph at
https://bitcoin-central.net/order_book (note: the current wall is not mine).
I understand the use of having more orders than the funds currently available for people doing swing trading. However, those orders should probably be kept hidden when they are not backed up by any money, as they give a totally bogus representation of the real market depth.