I bet it's a witch^W exchange's craft, ask/bid appears then immediate sell/buy happens, this is how you pump volume to attract customers. Hitbtc is/have been famous for this kind of advertisement.
ah. yeah. A while back it just jumped up to that one day and has been like that since. And someone had told me they were making a little money daytrading BIP, so I assumed that's what it was.
All the trades are fake you can notice it by looking at action, order book is untouched, all deals simply appears out of thin air you barely will notice orders matching marking history. it's selfish trading by exchange with 0 fees indeed or just a scam by pumpers trying to show fake volume and probably pump it.