@srm: Oh, okay. Then, yeah, my best guess would be wonky metadata.
To be sure, if you could PM me one of the 'broken' books (DRM or not, it's not an issue here), that'd help

. A log dump would also be helpful (type
;dm in the Home page's search bar, and send me the all_*_logs.txt files that'll pop up in your documents folder).
That should help pinpoint the issue

.