We just tried a fix for this where the book closer must make a full spell or he gets nothing. He still gets a negative if his spell is wrong, but if it's not a complete spell there are no partial points for him. Additionally, if the book closer fails in any way to make a complete and accurate spell he cannot close the book on the next turn. This completely eliminated the problem of people closing the book too quickly (for any reason, though specifically the cursed leader) and made the game play much better, in my opinion.
That variants seems to make it easier for everyone to make a complete spell.
I think the variant should be the Leader is only allowed to shut the book if they have a complete spell otherwise they don't move at all if they don't reveal a complete formula.