Why is "Assigned To Look Up" default sorting by Person ID?

On the Case page, when a Provider Group is chosen and then user clicks on the Assigned To Look Up magnifying glass, the search results display all active members of that provider group. The search results seem to be default sorted by Person ID; our customers have commented on the usability of this because the Person ID is not meaningful to them and some Provider Groups have a lot of members -- they would prefer to sort by Last Name. Of course they can click on Last Name to sort, but I was wondering if anyone else has had similar