Could you people read the stickied threads before posting an unnecessary thread?
Equipped items with the same power always take precedence over the cubed power. Working as intended.
edit:
25) Getting Less Benefit from an Affix when Equipped while also selected in Cube
When you have the same power on an equipped item, and in the Cube, the value of the equipped item is always used, even if that’s a lower value than the maximized value the Cube would give you.
-Credit Meteorblade