4_seven what Volksdevil is referring to is when you go to a second page.
On your test board if you Select PHP Skills 'Yes' then this initially returns 5 users with 3 on the first page. When however you try to go to page two your memberlist reverts to all 29 users rather than giving just the other 2.
The issue originally also occurred in my mod but I fixed it in a later version. From memory I think I fixed it by returning the search parameter back to the template in the way that normal phpBB profile fields searches do. Feel free to have a look at my code & 'borrow' any bits you want to help with a solution