Helmet decreases dps

So I just bought new helmet (pretty good one I think), but the problem is, that when I equip it, it actually decreases my dps for some reason :D I even do more dmg without helm, than I do with it! :D Keep in mind this helmet got int and dex, that scales even better than normal cause i have Hand of Wisdom and Action equiped as well. Is this bug or am I missing something? :D
Including screenshots - nothing else changed except what you see on screenshots


New Helmet


No Helmet


Old Helmet