Arrows Falling, Then Vanishing

Whenever I fire an arrow with a regular bow, the arrow stops, falls to the ground, and immediately vanishes.

Checking with "/testfor @e" tells me:
Found (username)
Found Arrow

I'm on a superflat world with nothing but a layer of Bedrock. If I stand on something else, the arrow does the same thing, but later shows up where it would've hit.