Unfortunately you have found yet another item that acts like this. I have found this with gorgon lens (depending on what type of scales they were made with) and potions of invisibility (which used to have a different hue and if you put both color hues on they bug the vendor) and I think a couple more items but I stopped reporting them a while ago. Now for the bad news, if you have logs in your inventory that are now forever stuck on your vendor, to ever get your vendor completely correct again you must...take out everything you can, remove your bid matching amount so you lose the stall, then wait (up to a week) to lose the stall, then wait (up to a week) until your inventory degrades and write off that bugged inventory that you lose as a lesson of what not to do. I have done it at least twice because of this type of bug and it will make you want to quit commodity vendors altogether. But for some reason I keep going back. Thanks for posting this new item.
http://community.stratics.com/threads/potion-of-invisibility-on-commodity-vendors.314930/
http://community.stratics.com/threads/commodity-vendors-and-gorgon-lens.300668/