When did the WoW client start creating .bak files for addons?

[Bringer]

.bak file topic came up when a user of an addon I maintain had problems because of the existence of a bad .bak file in his addon folder for one of the multiple accounts on his client.

I knew addons can't create .bak files and I don't remember having that file extension on my game machine (I stopped playing WoW quite some time ago.) I started to blame the curse client.. until I did more research.

I've spent lots of time searching on google and using search on Battle.net forums and here to no avail.

When did it start.. and was/is there a way to not have the .bak files created?.. Apparently the only way to have the client create a backup file for you is to start with a fresh clean directory... if a .bak file exists and you update the rest of the files for a new version of the adodn.. the client apparently doesn't know to create a new .bak file.