Can you manipulate the whip even though you cannot see it? If you can you may be able to fix it by droping it and picking it up again or swapping it in and out of a bag (though the bag option may cause more problems than it helps.)
I remember having this bug a couple times on another server a few bioware patches back, and I dont remember doing anything to fix it, but it ended up fixed... so if you cant manipulate it at all, I'm going to go with what L said. Try relogging and if it doesnt fix, just wait it out.