Toribash
This is likely because the colossal sword and nail bat are made for different joints, and so the game doesn't recognize them as overlapping.

It would probably be worth getting Fluxorious to clarify this however, as I believe he made the nailbat, and will have some idea on the colossal sword
As this is likely a bug, I'd recommend making a thread for this in the Technical Support Sub Forum found here:
http://forum.toribash.com/forumdisplay.php?f=11

You are more likely to get help there than you will in Rapid Threads.