A USER ON THE OFFICIAL FORUMS IS NOW CLAIMING THAT THIS IS A VIRAL INFECTION. Read more here:
[original post] Some VERY bad news. The most recent Borderlands 2 compatibly update (the one released for the Mechromancer) apparently contains some glitched code* or something that does just about the worst possible thing a game like this can do. It can permanently corrupt your save file, essentially deleting your character.
It happens like this: You get shot into a downed state, you die, instead of respawning either the camera endlessly floats around the landscape, or you're either booted out to the main menu. Either way, at this point you're most likely completely screwed. This can apparently happen even if you never download the new campaign DLC, but it's supposedly much more likely to occur if you are fighting either of that add-on's two new optional raid bosses.
Because of this, it is HIGHLY recommended that you backup all of your save games onto a USB device.
Here's a thread on the official forums dealing with this subject:
The good news is that the developers are aware of the issue, and are currently working on a fix. As said in another thread:
We are investigating this issue and hope to have this resolved as soon as we can.
In the meanwhile, backup your save games. It won't protect you from the badass rank glitch, but it could still save you from losing days and days worth of progress.
* Note that this was an assumption due to the glitch not appearing until after the update was released. It's now thought that another possible cause could be a result of modding. Read the forum topic for more info.