CSS quirk?

Here’s a quirk (I think) I’ve found in CSS (and Beel confirmed it):
If you’ve got sidebar menu items generically defined in the CSS under the #menu ul li ul li a (or a similar nesting), color, margin, and padding elements (and maybe more) are strictly governed by that #menu nesting, and even if you’ve got

elements nested within that menu that change the color or margin, etc., of a SPECIFIC element, the menu nesting trumps those subsequent definitions.
I had to reorganize my entire menu <div> last night because one specific

would not conform to the CSS rules, and thinking I was crazy, I asked Beel to do the same, and he found the same quirk.
So, any CSS gurus out there know what I’m talking about? And do you concur?
This was the nesting of my index.php:
<div id="menu">

blah blah blah
<li id="fubar">

<php call>

</div>
Is there sometimes an inherting conflict in CSS between div IDs and li IDs if the menu is grouped into one big

? I’m not sure what the issue is, I’m just stabbing in the dark.