Steps:

1. Play Book A
2. Pause Book A
3. Go to Book B
4. Play Book B
5. Power off (book will continue to play)
6. Power on, and look at iOS lock-screen player
7. Title and timecode will jump back and forth between the two books you have paused.

If you hit pause/play in the lock-screen, it will play audio for either one of the books, depending on when you tap play as it jumps back and forth between the titles.

See attached screencaps.