Save with serial letter not working properly

That's a very strange design. Furthermore, it does not agree with the description in the dropdown menu, which reads "Serial Letter (a, b, c...)". My alphabet has only 26 letters, yet even that number is more than I'm ever likely to need for a single image. If you prefer automatic appending of a number, you can choose to append a number from one to six digits. (Note that if you select a single digit, you have only ten names available, and to get ten rather than nine,  you must change the default starting number from 1 to 0.)  The selection for Serial Letter not only fails to conform to its description, but if the behavior were to be consistent with the appended numbers, then you should be able to provide a starting letter. If you use digits, each time you save the default starting number goes up by one. That's good design. What's happening with the serial letters is not. It's not really serial letters. It's the letter 'a' plus an underscore and a single digit. I've not tried to see what happens after a_9,