As a feral cat / tank I am using multiple copies of the same item, but with different gems and enchants. Now when I have my tank set equipped, and I open my bags, this will show my dps boots listed with the sets dps and tank. The boots don't group with my other dps items in my bags. This is just an example, the behaviour is the same for other items.

It looks like right now you're only looking at itemid. Any chance this could be expanded to look at gems/enchants as well?