[2019] Bug or weird feature?

So I have a question about the item shop.

I bought all of the current mythic heroes in the shop (lynx, subzero and wukong).

But now that I bought lynx and subzero they are still available in the shop (it says 1 left even tho I bought them already)

I also don't have the option to add them to the collection book, so my question is:

If I buy them again, will I be able to add them to the collection book, and if so, would it be worth it?

Thanks for reading, and sorry for my bad english.