Bound Players? Bug?

Where does it say anywhere that if you select a BND player from a pack that if you already own that card and it’s trade able that it becomes bound?  I bough coins to buy cover athlete package and selected 3 cover athletes.  I finished the weekly cover athlete challenges and picked one that I already owned and paid money for and you BND both of them!  No where, no where does it say it will BND every card you own that is similar.