Ah, I noticed that when looking through the report, just wasn't sure what it meant. I think I know what's going on.. maybe..
Might be something to do with the relation between optifine, IC2, and Tinkers Forge. Reason being that ic2 doesn't natively have a fluid cell of uranium, only the fuel cells. I believe tinkers forge adds a molten variant of uranium when used in conjunction with IC2. I also believe that IC2 has some sort of a general script for adding any fluids (mods or otherwise) to be able to be stored in its fluid cells (for compact physical storage). So with that being the case, IC2 adds the Tinkers forge molten uranium to its list of fluids for the fluid cell, and optifine didn't like that.
Although I could be very wrong about all this XP
Guess it's time for me to mess around with some config files!