Thanks to the many people who pulled me up on this by reminding me that that was a different astromech droid with Obi-Wan on Kamino, and R2 was with Amidala and Anakin the whole time.

Never one to allow such an egregious error to stand, I am working on a solution/explanation. Look for it in strip #214.

James Mishler suggests changing the tagline in this one:

"You freakin' idiot. What about the time I helped you, Qui-Gon, and Queen Amidala escape from Naboo? You don't own me, I own you."