Since everyone has come up with such nice, plausible theories, I have to be the devil's advocate. Conspiracy theory time!
Now, I'm sure more people than Vandar/Council/Bastila knew your identity. Remember the merchant on Korriban? "People talk" is his answer to how he knew who you were. "Three people can keep a secret if you kill one," right?
Regardless, not everyone could have been happy with the Jedi Masters' plan (which, admittedly, had gaping holes). They could have wanted revenge on Revan, or to prevent Revan from rising again. Someone could have leaked the coordinates and flight plan of the convoy to the Sith. Or, if it had been someone in the Republic fleet like Trask who knew what was going on, they could have neglected to remind the Council that there was a blockade on Taris.
Even discounting betrayal/vengeance from within, a Sith spy could have simply found the plans for a major movement of Jedi troops/Bastila and sent them to the Sith.
As for where they were going...Dantooine is most plausible. Tatooine is also an outer rim planet with a star map though, so perhaps there as well.