That's what I thought. Hmmm... If you have other iBooks are they all behaving normally, bookmarks working, etc.? If so have you tried deleting your new book and downloading it again? More here:
Downloading past purchases from the App Store, iBookstore, and iTunes Store
If that doesn't work the only other thing I can think of is to restart and/or reset your iPad.
[*]Restart the iPad: Press and hold down the Home button on the front of the iPad for few seconds until the red slider appears, slide this across to shut the iPad down. Restart the iPad by pressing the power button on the top until the Apple logo appears.
[*]Reset the iPad: if restarting the iPad didn't work then you will need to reset the iPad. You can do this by pressing the Home button and the Sleep/wake button on the top the iPad's case and holding them down together for at least 10 seconds, until you see the Apple logo. The iPad should then reset itself. The boot up process will take longer than the restart.