Oh yeah I've seen the same too. Price of BTC is at 1,110 seconds ago, but then change to 1,189 then 1,127. I don't know either if its preev, maybe just a normal movement in BTC price? It keeps changing from time to time.
Maybe its because that bitcoin price always change time to time, nothing stable especially when it comes to price. I dont know also if there's preev, maybe that's bitcoin, the price of it always change. A friend of my mine experienced this kind of thing also, and so i must consider the things that are possible to change especially in price matters.