Only one skill book dropped from radament, why?

A friend and I made fresh characters and killed radament but only one skill book dropped. Is this normal?

 

A book should drop for every character in Act 2 and partied that has not completed the quest. Try using a high lvl char and TP'ing the char without the book to Sewer 3 right before killing Radament.

I've done plenty of rushes where the chars were in town but a book still dropped for them, so if it fails to drop then something is wrong.