When you are in your user mail box and want to select all/deselect all it basically just reloads the page, it doesn't select any more.
The link to "select all" is as follows: http://xxx.xxx.xxx.xx:10000/mailboxes/list_mail.cgi?user=xxx# so it looks like the link says just to list the mail rather than to select all.
Which browser are you using there, and which theme?