My bookshelf page tells me two books are pending on members' wish list.

But My Account says only one is pending on a wish list.

I've never seen this before.

One is waiting for the member to accept the offer. That's the one you see on your account page.

The other book has been request, but is now in the 1 hour buyer's remorse period. If the member requests a book that was on your shelf, or if she accepts a WL offer and does not have the book on auto-request, then there's a one hour period after the request is made before you can accept it. During that hour, the book doesn't appear anywhere on your account page.

The book on "my bookshelf" is still marked "pending on a members wish list."

The remorse period passed a long time ago.

I think something is broken.

You might try contacting PBS directly and asking them to look into it.  You can use the Contact Us link under Company at the bottom of every page.

It's also possible that the first member declined and it has rolled over to someone else and is pending on THEIR wish list.  Sometimes a book can roll over to several people before it is finally accepted.