Not everyone runs a damage logger so that may explain why nobody else seems to know this exists. Basically when using the Igneous Weapons buff that adds fire damage to every strike the Forceful ability from the 2h tree does significantly less damage than it should. What appears to be happening is that the game is applying the 25% splash damage to the fire damage effect rather than the weapon attack. So I hit the second target for 6 damage rather than the 34 that I should be hitting them for.
This has been bug reported and CS ticketed, but as I have yet to get any indication that this has even been acknowledged I figured a forum post wouldn't hurt. Squeeky wheels, grease, etc