a command block have testfor @e[type=Arrow] {OnGround:1b} curently testing because of a redstone clock. When i shot a arrow and she hit the ground, the command block keep telling me: arrow did not match the required data structure. the problem is the command or a bug?
Ok I got it figured out. Playtested this and it didn't work for me either. Examining the arrow in a map editor revealed that the first word should not be capitalized. More importantly it's "inGround" not "onGround" or "OnGround". in.