Grease and Fist of the Titan

I do not know if this is a bug or a gameplay question. If it's gameplay, please forgive me. Fist of the Titan does not seem to be checked when grease tries to disarm you. I figure it should. There is no echo for it even giving an extra help to trying to keep the weapon. I figure it shouldn't be proof against grease, but it should give you a much better chance to hold onto the weapon than regular people. As it is now, there is no echo as there is when other things try to disarm me.