Why does the tooltip say an item is a X% upgrade, but it unequips after putting it on

[reynbow]

I'm an Enhancement Shaman

Example item: https://i.imgur.com/zzydlAI.png

Currently equiped item: https://i.imgur.com/tykSGLq.png

As you can see, the upgrade seems pretty obvious.
So why is it that as soon as I equip it, Zygor undoes it and decide to equip the heirloom item instead?

[ZG Support 1]

The gear system still likes to think that heirlooms are better for an xp bonus. While that is some-what true when you consider the rested bonus from the heirloom set it gives that a bit too much weight right now. You can safely just destroy the heirloom piece and then it won't try to equip it again.