I went to the city today and saw Bob there, which is surprising since he's a villager in my town... Is this supposed to happen? Has it happened to anyone else? Just wondering if it's normal

No, I don't think I've ever seen any of my current villagers in the city (and I've been playing regularly since launch). I've seen them shortly after they moved out, and I've seen them shortly before they moved in (particularly when online play was still supported), but not while they lived in town.

Interesting... I do wonder what's causing this, then. He also talked to me like any other villager in the city would, not that I would expect him to say something different anyway since they don't seem to do that after they move out (although I wish that was a feature).

Also, I saw Bob for a second time in the city today. It would be weird enough as a one time thing, but here he is again. I guess Bob is just destined for more than the small town life.

Have you recently played online (using wiimmfi, etc.) or used the DS Suitcase? I know villagers that moved out of one town can show up in someone else's city after multiplayer interaction. If Bob is using a custom catchphrase or wearing a shirt other than his default, that's a dead giveaway.

Hmm yeah, I do play online with wiimmfi, so that's a possibility. I haven't visited anyone with Bob in their town before seeing him in the city, though. Same shirt and catchphrase as well.