Okay, picture this;
Im on Zoric, by my house, there is tons of lag. I go to the gas station but the lag is so bad it sends me flying backwards into the sea for miles. I move forward and find that up sends me... UP and vice-versa.
Holy Crap
Most likely (from a recent bug report I think I read) it is a piece of landscape that is in the water, something that I'm not quite sure on. I've had the encouter with getting sent flying miles into the ocean because of lag and such, but never 'floating' in air. If you notice, the shadow under your vehicle leads me to believe that there is invisible landscape below you.