Cards converting to exp


I am not sure this is a bug. But after i opened my founders pack and had all those cards in my inventory, I then tried to add them to my collection. I got the warning that it would convert to exp if it exceeded the max enhance level. I didn’t know what that meant and clicked OK. It auto converted into exp. I did this with a legendary card, a purple card, and a couple green cards.

I have 0 cards successfully added to my collection. What did I do wrong? Is this a bug?