I am trying to remember but, I admit I am reaching a bit here…
I don’t have my 7.5.40 installed but, I seem to remember that a warning or option box popped up asking if you wanted to add a sequential number like you describe. Maybe this box popped up and you somehow checked off the option to do it. Then you also checked the option to “Please, don’t ask this again”.
If you think this may have happened (or if any of this rings a bell) check this thread out for how to reset the “Please, don’t ask again”.
Please note that I’m not a fan of deleting files so do this only if necessary. I have no idea if deleting this preference file just fixed the “Please, don’t ask again” concern or if it deletes a bunch of other stuff too.
It seems to me that Cubase should have a reset function somewhere in the Cubase preferences>general menu.
Regardless, if no one else chimes in here maybe your best option is to submit a support request.
Please report back if this worked or how you fixed this (if you ever do). Thanks 
Regards 