Menu ancestory when a page has more than one menu entry

I am having a problem with the menu ancestry in two situations:

1) when a menu item occurs more than once in the same menu

Sample:

• Item A

• Item A1
• Item A2
• Support

• Item B

• Item B1
• News
• Support

Support occurs in both Item A and Item B menus, which results in both Item A and Item B receiving the ancestry classes (current-menu-ancestor current-menu-parent).

I need some way to remove the ‘current-menu-****’ classes from the duplicate menu item.

2) When I am on a category detail page.

Example: If News above is a category archive, then when I am on a post page filed under the News category there do not seem specific classes that allow me to highlight both Item B and News.

—
I thought perhaps a custom walker looked promising, but at this point I cant wrap my head around how to determine the true ancestory (based on page heirarchy and/or category) for the current page.

Any help appreciated!