I still feel this is sort of a bug, but I'm going to try submitting an idea.

When logged in: You can click on any link in "My Bookshelf" to expand it, but you can only collapse it by clicking either the down arrow or the "My Bookshelf" tab. When on another tab such as "Bookmarks, Saved Searches, or Reading History", I feel that clicking on these tabs should also collapse the My Bookshelf back to the bottom.

When not logged in: Clicking any link in the "My Bookshelf" will expand it but clicking "My Bookshelf" no longer collapses it - only clicking the down arrow will collapse it.

I feel this can be confusing for the user - Thank you!