In SoulseekQt, the sort order of the Unshared user list can be toggled by clicking on the User column header. The direction of the arrow is wrong (it should point upward for ascending order, e.g. A to Z, and downward for descending, e.g. Z to A), but the sort toggle works, at least.
It would be nice if this functionality were available on the Ignored and User List tabs as well.