I got Trommel's sword.. killed him and looted it cause I was under trhe impression it was a bastard sword.. however, it shows up as a greatsword when i try to equip it. before it was ID'd, it said "Prince Trommel's Magical Bastard Sword", then I ID'd it, and it became a greatsword. Also, I was under the impression from a gamefaq faq that the reward sword you get was also a bastard sword, and indeed, when I got it, it said Magical Bastard Sword or whatnot.. then i ID'd it and it, too is a greatsword. kinda annoying.. I wanted my rogue to wield both.. 5d6 sneak attack + the 2 swords..
it should be a bastard sword. Did you take the weapons proficiency otherwise it can only be held two handed which may be your problem