Hi,
In PTE AV Studio 11 we introduced a new option in the Preferences > Project tab:
Save a copy of .pte project file in a .bak file
Currently, it's not ticked by default.
You'll always get a previous copy of .pte project file before last Save command in a .bak file. It's a renamed project file.
In case of any problem with .pte project file, you always have a copy of a project from one previous step.