Headers for collapsible form boxes show up below their content

[Found using Firefox 1.0.6 on Mac 10.4.3 -- haven't tried any other browsers]

Go to any node edit page (node/x/edit). Pick a group box that is collapsed and click the disclosure triangle for that box.

Actual result: Title for the group box moves below the content that just appeared.

Expected: Title remains at top of group box.