This is very odd... every time you try to add ANY ability to the Spell Book, and give the Spell Book to the targeted unit, it drains all their mana. I tested with other random abilities, too, in your map... Critical Strike and Spiked Carapaces also drained all mana, even when they were the only spells in the spell book.
My only workaround, really, is to give the unit the Spell Book when they are picked, and then do 1 of 2 things:
1) Set level 1 of each ability to do nothing, and level 2 = level 1, etc. Then you can just keep them with the Spell Book having the level 1 abilities, and it won't do anything. And then in the trigger, set the level of their abilities to the level of the casting unit's ability + 1. Or...
2) Keep the Spell Book on this unit the whole time, and just disable the abilities inside the Spell Book for every player, until the ability is cast on them.
Sorry, I know that isn't a great workaround, but it's the only thing I could get to make it functioning, besides just adding the Mana back.