No bug, but the manual entry here https://www.scirra.com/manual/61/preferences is not clear enough. It does actually state:
[quote:do45vcnl]In the event of a crash, power failure, or even just accidentally closing and not saving, the project can be recovered from the last autosave by opening the .capx.autosave file.
No reference is made to renaming the file, so new users will not know what to do in the event of a loss.
Maybe Ashley can add an automatic option for loading the autosave file, or at least amend the manual to let users know they will need to rename it before attempting to open it.