I've seen a lot of floating land formations but this seems a little too odd. The seed is "-7302058265901491281"
x: 55
z: -5
This formation was naturally generated by the game in "extreme hills" biome. Half of the formation is in the "Stone beach" biome, this may be unrelated but It might be the cause of the bug.
If this is a purposeful feature then I apologize in advance.
Environment
Windows x64, Java 7 u21
Random terrain generator is random, I'd say, since I get it too.
Looks a bit like Africa. Weird, huh?