This is Hotties for Sale (app id 105848).
Here is what is happening:
Case 1: Users A, B, and C go to view the profile of user M, but the page displays the profile info for player X instead. This persists for a certain amount of time (a couple of hours) and eventually M's profile will reappear. This happens with the profile surface.
Case 2: User N logs into the game and gets user data for user Y (canvas surface). User N can chat/buy/whatever as user Y. Some people try to uninstall and reinstall when this happens, but the wrong user data persists, again for a couple of hours.
The only types of caching/persistence we have running are session cookies and mySQL stuff. A session collision wouldn't explain case 1, where all users get the wrong profile data.
If this is MySQL corruption then I wouldn't expect it to automatically fix itself after a couple of hours. And it is the user ID that is wrong, which comes from MySpace.