I've not seen this on the wiki so I don't know if it's a limited issue or if nobody has noticed it before since it's very easilly missed. I've been able to do this twice and on each occasion it happens in exactly the same spot regardless as to what faction I'm working for or position in the main storyline.

During the Vault 11 mini quest, when the sacrificial chamber is opened and you head down the corridor you hear the line "Walk to the light, the light makes you feel nice" etc. Theres then a bright light and if you keep walking you end up in the chamber.

Well... when theres the flash out, the game access your saved data utility and makes an unauthroised save. This is not an autosave, nor does it over-write the previous save file I've been using, it's a brand new save file that the game has made without authorisation.

But would you believe that this bug seems to have it's own bug. I mentioned earlier that I did this twice, the first time I continued on and finished the legion ending, but I never over-wrote the save it had created, so it was still in my saved games folder as a seperate file state.

However, going through the stage again on a 'pro NCR' run, the game made a save again.. but over-wrote the original one it made in this area, I know it's done this due to the date/time stamp of the save, and that the original save it made at this spot has gone.

So what you might ask.

Well... In just about every game you play, especially one as complex as Fallout, a save typically takes a short period of time before it's finished, when you make a save in Fallout the game prevents you from doing anything, for quite a while... Even an autosave, if you pause the game, you cannot select Save or Load for a long time. It's possibly the reason why you can't play casino games just after you load or save a game. But this save takes barely a second for the game to make. So it might not be stable and subject to corruption if you attempt to load from it or save over as it hasn't followed the normal opperating proceedure for a save to be made to your PS3.

However, don't forget that in a number of places on all 3 versions (mainly the 360 mind), theres a bunch of places where saving can cause a huge save file corruption, the majority of these places are inside vaults and in areas close to or around the overseers office. Meaning that if your game makes a save point here, the file could end up causing you problems in the future. If you do enter this location and find the game has made a save (again it might just be my system/copy) I would strongly advise against over-writing it or making that your new main save file, ignore it. At best it's just a normal save file that you could use, but given all the problems that can occur from saving in vaults by the overseers office, I wouldn't want to risk playing with a save file that you didn't want or create. If the game is attempting to make unauthorised saves in vaults or other areas, it might explain why there are faults/corruption errors, because the saves are incomplete or corrupted due to the player still being able to do things/progressing when the game should pause action whilst the HDD is accessed.

Also if anyone hasn't done vault 11 and entered the chamber yet. Could they test this out to see if the game makes a new save file for them?

It's called a scripted auto-save. Consoles can't turn them off since you don't have access to the INI file.

They are intentional and designed to save you in case you didn't make a save on your own recently. Vault 11 is one of the places that the game makes them, but there should be others.

Savegame corruption is a big issue, but it should be less of an issue for these saves due to them not being overwritten very often. On the PC, though, a lot of people still recommend turning them off and relying only on hard saves you make yourself.