It really seems like a bot is constantly buying, like with Mt Gox. But I wonder if that is the case, or it is just general buying pressure from new investors.
Everytime an exchange is hacked for BTC, they need to recover those by re-buying them, just like Gox was trying to do. (Excluding any permanent hair cuts) we know of lots of hacks in most of the major exchanges, there are no doubt some we don't know about. As the price starts to climb, it makes sense to step up the frequency and quantities of the buying bots to capture the coins at the lowest price.
Many people , including myself independently spotted willy bot, but times have moved on and with a little thought and programming its going to be almost impossible to see them in action, but its got to be likely that they are contributing to this rise.