The user directory does not list filter options for StaticList properties

Steps to reproduce:

• extend the user class XWiki.XWikiUsers with a new StaticList property "mylist" with options like "alice=Alice|bob=Bob"
• customize the user directory to display the new property "mylist"
  Result:
  The user directory does not list any filter options for "mylist" because while, it is built using a custom results page, the "class' parameter has not been specified for the column properties.