PDF's disappeared from iBooks

[Getitdone]

iPad with iOS7.0.3. Opened updated iBooks to PDF's and they were all displayed and then suddenly disappeared. Checked around in iBooks and found all of my books, but PDF's seem to have vanished into thin air. Has anyone run into this/ have a solution? Thanks.

 

[Brammy]

Double check "sync all books" is checked in iTunes.

I've noticed sometimes it gets unchecked.

 

[Getitdone]

Double check "sync all books" is checked in iTunes.

I've noticed sometimes it gets unchecked.

Thanks - all were checked to sync. They do show up on my iPhone so at least I will be able to easily move those to my iPad. The PDF that I added to the iPad last night is still there so hopefully it will be okay from here on out.