This issue is still occurring, but I've found a workaround. If the Sim cancels the reading action rather than the player, they get credit for the goal. The easiest way to do this is to queue up an action that requires them to put the book down, and they'll put it away on their own, especially if they've read it before.
This worked! Thank you, thank you so much for posting this answer. For the record: had her reading the (Neverending) Ultimate Tome, queued up making a Plasma Jane, she dropped the book on her own and voila: instant complete.
PS: Did I say thank you? 🙂
