Not necessarily wrong, just you can only have 10 of the 11. (Thought this post was about Lone Wolf Gamebook 22 first), the other classes in Heroes of Magnamund have just ten powers to choose from I agree. Perhaps the advanced bucaneer character, up to rank 20 in line with Magnakai, will let you have 9 other powers and the one you are missing must be taken at rank 11?
Lightmage's suggestion is a good fix if you don't like this.