In truth, Mithras wasn't surprised. From the moment he'd met Odoacer in the Blood Forge, the dragon youth knew that he faced his father. The looks might be different, but speech and manners didn't lie. Two people couldn't talk and behave in the same exact way, much less men from such different backgrounds. So for Odoacer and Mithras' dad to project the exact same sensation could only mean one thing:
They were one and the same!
As for why Mithras didn't get that sensation from Ricimer or the original Hadubrangr, it was simply because in those incarnations, Odoacer's persona was vastly different. Moral and upright in one, but incomparably violent and decadent in the other.
Vel'Asha, however, hadn't seen this one coming. And for good reasons.