lets say we have this menu:
Home: / About (page): /p=10 A Category (archive): /cat=8 A post of cat num 8 (post): /p=101
If we go to "A Catogory" - Yes, the li has .current-menu-item class on, and thats good!
But if we go to post-101, the parent-category is not highlighted in the menu. So thats 1 problem.
Lets view another example with menu-childs:
Home: / About (page): /p=10 --> A Category (archive): /cat=8 --> --> A post of cat num 8 (post): /p=101
if we go to "A Category" or "A Post...", the menu-parent (About) has no .current-menu-item class as well.
That feature is required.