Trying to avoid a spoiler Vometia, on the shambling oak...I think I know what you mean but there is the nasty unforeseen effects from that item? or maybe I am missing something...wouldnt surprise me in the least...I have looted it by accident and immediately regretted it. I could be doing the other quest in the wrong order!
If you haven't yet done Brandon's quest (the one where all party members can learn to safely handle tenebrium), you can use a handy star stone to rid yourself of the annoying effects of the item in question. After you've got rid of it, of course! I find that by that sort of point in the game I generally have one or two going spare.
