the forums are crawling with posts regarding "navbar-inner" not working properly. i'm willing to hazard that everyone who's experiencing these problems is using "float:left" to get the primary links to appear inline (as opposed to "display:inline). in this case, the navbar-inner needs the clear-block class, or the float elements (the LIs) will break out of the container.
i fixed this in my own sub-theme by adding the clear-block class to the page.tpl.php file, but it really should be added to the theme in general and to the starterkit. clear-block is applied to all other divs that contain floating elements (main, header, etc).
anyone know how to get this done? it's relatively minor but it'll keep a lot of folks from baning their heads against the wall.