The Advanced Menu 1.3.0 (update 8 Feb 2012) has a bug, when displaying a selected menu item, being that 2 items display selected at the same time.
The bug is related to URL matching of the pages.
You have a "custom" page and "custom-sample" page and add them at the same level.
The advanced menu is matching the "custom" word in the URL and thinks that "custom-sample" is a child of "content" menu item, putting the classes "current" and "selected" where they shouldn't be.
To fix this temporarily, until a fix version is released, you can rename the pages URL, to another not matching words.