Have you talked to Brandon with the character who actually has Tenebrium in his/her inventory? If - say - Madora is carrying Tenebrium and Roderick initiates the dialogue, then you do not get the appropriate text lines from Brandon.
I just checked it. Roderick has the Blood Stone Cage, which has the tenebrium bars. He is the one who talked to Brandon, who still does not acknowledge that I have the tenebrium.
