A customer had this last week too, and I hadn't spotted why it went wrong on their site only - but it was the same scenario as yours, so I can see it is the A-Z interface injecting an extra variable and throwing off the code.
Please try the attached sources/urls.php.
FYI we will improve the usability of the A-Z thing a bit in the next patch release, as I found it a bit clunky when debugging this.
(Click to enlarge)
#1446 - Duplicate Header on Members Page
A customer had this last week too, and I hadn't spotted why it went wrong on their site only - but it was the same scenario as yours, so I can see it is the A-Z interface injecting an extra variable and throwing off the code.
Please try the attached sources/urls.php.
FYI we will improve the usability of the A-Z thing a bit in the next patch release, as I found it a bit clunky when debugging this.