The Strongbox Mirror of Kalandra drop, is it a bug?

After the new patch the strongbox got buffed but the drop can be influenced by rarity now. And I heard one 6-player mf team ave. 25 turns will drop a Mirror. It maybe the reason that after new patch the Mirror priced dropped from 500divs to 260divs. And I really don't want the phenomenon of currency inflation like in PoE1 happening again.