Does this large furnishing item actually increase your spell and weapon critical by 3.5 % somehow just be having it in your house or is it some weird glitch/ game error throwing that in the description.
That definitely looks like a bug to me. Go ahead and report it in-game with this information please! I've passed it along to the Devs but it's good to have it go through the proper workflow as well so nothing slips through the cracks.