In the video below, three astronauts on the ISS are demonstrating to us lowly earthlings what happens when the ISS accelerates in space and boosts itself into a higher orbit. As you can see, they hilariously start to get sucked away.
What's happening is that because the space station is accelerating, people and things inside the station aren't adjusted to the pace of the acceleration (or as adjusted as they would be if the station was travelling at a constant speed). So things that aren't tied down inevitably float backwards because the station is moving faster than they are. Think of it like riding a subway and how you have to brace yourself when the train starts up versus when you're chilling as it's cruising. Or an aeroplane. Whatever! That's my semi-scientific take on it, at least.
But my quacky science aside, I'm just happy to see Expedition 29 Commander Mike Fossum and engineers Satoshi Furukawa and Sergei Volkov floating around and having fun with it. Sure, it's more than a little nerdy but you're in freaking space, who cares! Enjoy it! Trip out at how you get seemingly sucked backwards. Cannonball zero gravity. Tumble. Flip. And then do it over again. So awesome.