Popup still appearing after Close button acts as... is set

The popup is still appearing, even though i have set 'Close button acts as 'Never see this message again' link'.
when i click the 'never see this again link' it works fine, but when i use the close button (x) it will come back after a reload.
i have already read through other threads about this, and i have set the timeout, but it didn't help.
i have also set my nginx settings to:
if ($http_cookie ~* "^po_.*") {
set $no_cache 1;
alltho this shouldn't be related at all, since the regular 'never see this..' link works.

any more ideas?