That's odd. Usually NO spark when away from block (Electric needs a path to ground).
I can't see where the spark would be going to.....When the spark jumps the gap, it has to go to ground. If it is in the air, and you are not getting shocked, it seems there is something missing in the description.
Maybe someone else has seen this...
The only though is the spark plug wire insulation is conductive, but that still wouldn't explain it going away.
Another thought, try a different plug, maybe the one you have is grounded internally, and is sparking somewhere besides the tip. I have seen that before. A crack in the porcelain under the metal nut area that is not easily seen.