[Plugin: Post Expirator] Box does not display or can't move box

On a site that was just upgraded to wordpress 3.1, the post expirator box (on the add/edit post screen) does not show up for me at all. For other users, it shows up but is laid over the post content box. In those cases, they can move the box, but then next time they are on the screen, it’s back where it was (its new position isn’t remembered). This makes it almost impossible to use.