I've created a custom post type for products and a custom taxonomy (category) called brand associated with it.
Going to the "brand" category editor worked fine (I could add in new brands) in version 3.04 but after the update to 3.1.1 every time i click on the Brands menu item in the custom post type I get directed to a page that says 'Cheatin' uh?' with nothing else on it, apparently it's a wordpress error page.
To test this i created another custom taxonomy and associated it with pages and when I tried to edit it I get shown the same 'Cheatin' uh?' page.