Memberlist ignores sort when hiding search form

When I go to the memberlist and click on: "Find a member", the search form to seach for a certain order of the memberlist does appear.

But when I change the sorting of the memberlist to postcount and let it be Descending everything is right. But when I click on: "Hide member search" it goes wrong. The memberlist displays me the newest members and not as before the members with the highest postcount.

This problem only appear on phpBB.com by me. On my own board and phpBB.nl e.g. everything is working fine, so that's why I post this bug here in the website tracker.