Is it intentional that the arena didn´t reset?

You should really learn to read their news articles.

“Crafting a card counts towards acquiring it, and any cards you acquire and later disenchant (whether golden or non-golden) count as well. This means that if you get a card that you don’t want, you can disenchant it and you will not receive it again until you have all cards of that rarity from that set.”

It´s from their blog. First read all, then ask questions.