Having an interesting evening of
Sleeping Dogs and
XBL buggery:
Last night I played offline, and used a memory unit stored profile to do it.
When I played tonight, I booted my 360 without the memory unit, AND online, where it updated from the server, I guess. The Achievements I made last night were not on the XBL servers, but they were on the memory unit version of my profile. I played for about three hours before noticing this. When it popped an Achievement which I already had, I thought "Hm, that's odd."
When I rebooted the 360, where it should use the memory unit-resident profile, but the Achievements were still gone. The more recent gamertag data is likely given priority.
So I reverted to an earlier save game data, completed the one Achievement which would be otherwise impossible to get without a substantial replay (lucky!), then popped back to the normal save.
BACK TO BUSINESS AS USUAL, I thought, so I cruised out to get some Curry Fish Balls or whatever -- at the button prompt TO BUY FOOD, I was warped into a bus, the map came up, and I was told to select a destination. I tried to Cancel out, and was then shown as a passenger in the bus, riding around wherever the driver was going.

The button prompt to buy the food was also still on the screen.
I've just reloaded again, but am thinking it's probably time to call it a night.