TOPIC: Attendees list not sorting correctly on custom field

We added a custom field to capture the year an alumnus participated in our program. the filed is a dropdown type, with all of the program years listed in the field definition. I've also added the field to display on the front end attendees list.

The issue is that when I try to sort on that column in the front end attendees list, it won't sort properly, the years are all out of order, e.g. 1977 is sorting higher in the list than 1970.

Thanks for any help in advance!
-J-

PS: you can see the list here: uwpiaa.org/AlumniEvents/index.php/compon...roller=event&Itemid=