To see this bug you need to have a decent amount of content in Personal Books.
You need to do a search for some common word or phrase that will have at least a screen's worth of hits in the My Books section (which must be expanded), as well as pages worth of results in Library Results.
Scroll down to the bottom of Library Results and click "Next" to go to the next page of results.
The results screen scrolls back up so you're looking at "My Books" hits again instead of the next page of Library Results.
See screencast for a demo/explanation of this: http://www.screencast.com/t/oNISX3Ox