So I made an arena deck using some upgraded and some unupgraded cards in it. A day or so later I upgraded a card which was also in use in my arena deck. It was removed from the arena deck and left it with only 34 cards in it. When i went into editing mode It wouldn't let me resubmit the deck with 34 cards in it but if i left the deck as it was and played against the deck it only had 34 total cards. This could potentially be exploited to make an arena deck as small as you like (If you are prepared to spend 1500 electrum for every card removed)
