I'm using Themekey with Context to enable one of three different themes on a site, depending on a themekey field. The homepage is set to use my main theme, called 'sitetheme'. Sitetheme is set as default, but many themes are enabled.
All the pages that I've tested look good, including the homepage. There's just one exception. My main menu, a horizontal header region menu block that uses Nice Menus to create dropdowns, has weird styling on it. When I inspect the element, I see that it has styling applied from a CSS file that lives in a different theme than the one that is enabled on the front page.
The front page is also of a nodetype that doesn't have the themekey field that some of the nodetypes have, that can be used to override the theme.
Why is my foo theme's CSS for Nice Menus getting applied on pages that use Sitetheme?