Equiping helmet decreases my 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

bump

Try using the correct forum , you might get a response.

This is the POE1 forum.

My guess is the usual suspect: accuracy rating.

The damage, if I'm not wrong, is calculated as an average damage per second (PoB calculates average damage per hit individually as well, but I think PoE doesn't).
This means that less accuracy rating = less attacks you land. An attack missed is a zero, so that lowers your dps by a ton but not necessarily your average damage per hit (which is not shown in PoE).

This explains why a seemingly better helmet lowers your dps calculation but why does having no helmet seem to lower your damage? My guess is attack speed. More attacks per second more chances to have missed hits. More missed hits (zero value) less average value.

Fix your accuracy rating (cap your hit chance) and this shouldn't happen anymore.

The old helmet did not have max life. The new helmet does. Equipping the new helmet increases your max life, but not your current life, so you are no longer on Full Life.

There are two passives which increase your melee/attack damage when on Full Life: Initiative and Killer Instinct.