If you add Greater Conflagration potions to your commodity broker, it is immediately returned in commodity deed form as an invalid item.
This also happens for greater Confusion potions!
submitted to uobugs
Sadly, just checking on some old bugs with regards to the commodity vendors and this bug still exists.
Not quite a year but I had hoped they looked into this when they added the etals of the rose of trinsic and such to the stuff that commodity vendors could sell.
Also there are more things that if you add it, they claim it as invalid item and return it in commodity deed form immediatley.
The latest I found was sweet dough (though regular dough works fine) but I don't have a complete list.