Sorry for being misleading by reporting a bug so that I could propose a new feature, but I thought this would be the only way to reach you. So, in a nutshell, my idea is that when you combine an enchanted book with a weapon or tool, all tags on the book would apply to the weapon, besides just enchantments. So if the book has the Unbreakable tag, the weapon or tool would be unbreakable when combined with the book. I think this would be very useful for mapmakers and servers. If enchanted books have other tags for books only, then add a compound tag "ApplyTags" that contains modifiers and enchantments separate from the book-only tags. Maybe you could also add a tag "RemoveTags" that removes tags with names matching those in the list from the weapon or tool of choice. So a mapmaker could make a puzzle map where you have only one tool throughout the map, and you have to enchant it with enchanted books in each level to get to the next one, and every time you enchant the tool it receives new CanDestroy tags, but loses the previous ones. The only problem with my proposal is balance. If a book has the Unbreakable tag on it, then what is the cost to enchant it? Is it no additional cost because the book could only have the tag by using commands, and would be harder to enchant on a map? Or does it cost an arm and a leg because the tag is so valuable? Or... Maybe you could have a tag "TagCost" that changes the cost of each tag, or a tag "CombineCost" tag that is the cost of all tags and can be customized, and if missing, will default to the cost of all enchantments on the book and ignore the other tags' cost.

So anyway, thanks for listening to my proposal. Even if you don't decide to add this to Minecraft 1.9, I'll still look forward to it!