Which version of KotOR are you playing, and on what system? I have seen this bug mentioned before elsewhere, but I've been playing v1.03 (unmodified) on Windows and when I check Messages - Feedback I see the expected Dual Wield Penalty in the Attack Breakdowns for both main and off hand when using any double weapon (Quarterstaff, Gaffi Stick, Wookie Warblade, Double-Bladed Sword, Vibro Double-Blade and Double-Bladed Lightsaber) with or without Two-Weapon Fighting feats for player, party members and enemies.
There's no direct mention in SWKotORv103.txt but it might have been fixed, perhaps inadvertently, in v1.02 as a result of the following: