I'm using the Twenty Ten theme and a custom menu. It has been working fine for several months; adding, moving, changing menu items, no problem. Today I tried to add a new page as a top-level menu item, and it turned the last top-level menu item on the list from 'page' to 'custom'. Doesn't matter what new page I try to add - the last menu item turns from 'page' to 'custom'. I only have page items in the menu, nothing custom.
Any ideas as to what's going wrong? All ideas appreciated!!