Pulling out a combat knife from the boots does not work properly - you need to pull the knife to the hands and relog to make the knife appear.

Even after a relog I had several problems with fake clones of the knife and it was impossible to put the item out of the hands back to the inventory. Only throwing the knife worked to get it out of the hands slot.

Eventually I lost the knife although I put it in my inventory - after the next relog it disappeared.