This is new behavior that started with 12.7.3.
I can make any other change to a filename -- add or delete single characters, change the name entirely, run any preset -- and the filename retains its position in the file list. If I change the case of any letter, though, it moves the file to the end of the list. So 'abC.jpg' changed, eg, to 'aZC.jpg' or 'Cba.jpg' will retain its position in the list, but changed to 'aBc.jpg', it moves to the end.
It's kind of screwing with my workflow; is there way to stop it from doing this?