The way that the first and second sidebars affect the layout depending on if there is content in either of them kind of makes sense. You might have a page with no sidebars, so it would be nice if the content expanded to take up that space.
But for the navbar, this kind of functionality makes little sense. Either the entire site has a horizontal navbar or it doesn't. I've never seen the use-case of some pages having a navbar and some not. This has the side effect of making our page.tpl and our CSS more complicated then it needs be.
PLUS, if you are removing the navbar from your sub-theme, you really should delete all of that code in the page.tpl since it will never be used. But since some of this mis-feature's PHP is in the #main div, its easy to leave bits of the code that should be removed or to delete too much.
If we make the navbar always show. Then it is REALLY obvious how to remove the navbar in your sub-theme:
- Delete the #navigation div and its contents from page.tpl and maintenance-page.tpl
- Remove the CSS from your layout stylesheet that talks about #navigation.