Custom page slug is lost (reset) upon save

I have a WordPress 1.5.2 site with several authors. I’ve given some Pages a custom slug, but these are lost (replaced by the default slug-from-page-title) after the Page is edited by a Level 5 user. (Level 5 users can edit Pages but not the slugs.)

I’ve noticed that at least one Level 5 user becomes the Page Owner after editing a Page created by another user — is this normal?

Has anyone seen this before? The slug hijinx bothers me, because it breaks the existing links.