The same thing happened to me in the Shanghai mission.
My Xbox 360 console locked / froze up as soon as I got into the Tank.
After re-booting the console, it told me somethign like my game file was corrupted adn I would have to start over, so back to Baku. All my dog tags / weapons unlocked were retained.
I have had the Shanghai misson lock up 4 times so far shortly after I get into the tank, but thankfulyl only one time did it coprrupt the game file so that I had to re-start.
