The user directory search options (free form text and group selection) do not function when the sort column is a custom user field. The search clearly runs, but the returned results still include all users no matter what is searched for or what group is selected. If I select a standard field (username, posts, replies, etc), the searching functionality works as expected once again.
In my use case, I have two custom user fields displayed in the directory, both of which are of type Text Field and both are searchable. Running version 2.9.0.beta1.