When selecting items in the inventory, they stay highlighted even if you take no action after clicking on them.
Example: Shield A is equipped. Click on shield B, popup comes up giving the options to equip, compare, etc. If you click on the screen without selecting an option the dialogue closes, but the item stays highlighted, in addition to whichever shield is equipped.

In the case of armour and helms, three items can be highlighted this way, for worn, costume, and last clicked on.

Kind of confusing...