From what I understand ... these items all got set to 0 value after purchase so the player couldn't buy the house upgrades, have them applied, and then sell the papers back to the vendor.
However, the furniture does not actually get added till the player exits the transaction. So if the player instantly sold the items back to the vendor, they would effectively break the housing system by "giving away" the item before it could actually have its furnishings applied (since vendors don't offer to sell such items again).
It seems the original Unofficial Oblivion Patch adjusted these so that they didn't even show in the trade window after purchase, preventing the player from being able to mess this up. However, this one particular item now shows in my trade window with a 0 value.
As a side note, it seems Oblivion Remastered tried to fix this by different means; the notes maintain normal value so they can be exchanged back and forth till the transaction is exited. Then the furnishings are applied and the values are set to 0 simultaneously. However, as I noted on UESP's Housing page, they missed some of them.
So I don't know if the this particular sitting area note was missed by BOTH the Remastered team and the Unofficial Patch team or what.
Issue Data
Issue #35312: House Sitting Area Item for Skingrad Can Be Sold Back to Vendor