Unable to use custom dropdown field for sorting

[Louise Baker]

I've created a custom field (Select List (single choice)). However, I can not properly sort by this field. If I choose it to sort, it doesn't actually sort! (The view does not change).

Additionally, I know that this field is not filled in for every ticket, however if I search for <fieldname> is EMPTY, nothing returns.

An additional Select List (single choice) custom field properly sorts on values in an issue filter.

Any suggestions on how to remedy?