Upgraded to 6.x-1.5, now wrong menu is showing up!

I just upgraded SimpleMenu to 1.5 on two sites I maintain, and now the menu bar is no longer displaying the Primary Links menu as it's supposed to - it's displaying the Navigation menu instead! Which breaks the site layout completely, since that menu is too long to fit in a single row in that space.

I checked the module settings (admin/settings/simplemenu) and it's set there to Primary Links, not Navigation - but Navigation is still the one that displays on the page. I tried resaving the settings to see if that would correct it, but no.

Has anyone else encountered this? Does anyone have any idea how to fix it? For the time being, I'm going to try going back to an earlier version, but that may just break things further... :( I really, really don't want to have to restore the entire site from a database backup if I don't absolutely have to, particularly since I just updated a whole bunch of things (none of which had any relationship to that menu, so I don't think it could be anything else), but I may not have a choice.