I'm going to join the growing chorus of voices suggesting that something's not quite right with Qui-Gon. This isn't a fully-developed explanation, but keep in mind that Qui-Gon didn't vanish when he died. Neither did Darth Maul, or Anakin/Vader. Obi-Wan and Yoda both did. When asked about this after TPM, Lucas indicated that it would be addressed in subsequent films at some point. Also, we now know that Qui-Gon was Dooku's apprentice. Doesn't prove anything, but still... Finally, Qui-Gon was totally gung-ho about Anakin being trained as a Jedi, something disagreed with by the Council, and especially by Yoda and Obi-Wan (who ultimately relented, but possibly only to keep his word to Qui-Gon). Also, Qui-Gon spoke about Anakin bringing "balance" to the Force. Doesn't mean he would necessarily be the GOOD side of the equation. Could also explain why Obi-Wan never mentionned Qui-Gon to Luke (I mean, beyond the likely fact that Lucas hadn't written his character yet).