I believe it was a problem with crew communications. The official who had the flag for illegal forward pass didn't know the ball had hit the ground, and saw a crewmate signalling "touchdown".
The official who signalled "touchdown" didn't know if the loose ball was because of an illegal forward pass or a fumble (in which case the TD would stand), and wisely let the play continue.
The problem came when they got together to discuss what had happened. NO ONE on the crew ever said that the ball had hit the ground.
Of course, the rule misapplication allowing an untimed down should never have happened. That crew will not work any more playoff games for 2008 or 2009, and have been placed on probation for the 2009 season.
And,
FWIW, I'm
sure that they would have gotten it right if Jake had been on that crew!