Well if its burnproof and your fighting a zerk, weapon cleave effectively becomes disarm? That seems to be just a bit overpowered if you can not only cleave, but grab the weapon to? I say that burnproofs should not be able to be cleaved period, thats what the burnproof flag means, unable to be burned:). I say that weapon cleave mechanically works perfectly, maybe some type of message to let you know the weapon is burnproof and if you try to cleave it you damage your own weapon a bit (like a failed enchantment with enchant weapon) lowers dam dice, or avg dam a bit.
Cleaving
The problem that I see with the suggestion of having a disadvantage to trying to cleave a burnproof weapon/shield is that you can never know if some are burnproofed or not. So if you see a weapon that is normally not burnproofed, but is in this case, and you go to cleave it, should you be penalised any further than just the two rounds of lag, for something you cannot know about in advance?
Again, cleave doesn't need boosting at all. Take Path of Fury, powergrip an axe/polearm, and go cleave. It lands an awful lot. It is also more powerful than disarm in the respect that you are outright destroying your opponents weapon/shield, not just disarming it, and you can cleave nodisarms providing they aren't burnproofed. But the way it is now, you might waste 4 rounds of combat doing 2 cleaves against a burnproof that you don't know is burnproofed (because like I say, there is a way to burnproof weapon/armor without having to use sockets) and put it down to bad luck on your part, and go for another.
By having a message that simply tells you, if the cleave would have normally been successful, that the weapon is burnproof, it stops the Zerk just wasting time trying to cleave it.
Dey
why to the inventory? wouldn't dropping it be more logical? (unless it is nodrop)
Its a balance issue - zerks can't disarm for a reason. How easy would it be for fg zerks to get that fire lance if this was implemented?
Dey: Sorry for de-railing your thread. I think its a good idea to implement the message, its really no different from what you see when you suceed disarm vs a cursed weapon.
Cheers,
L-A
PS - Dey, you can make any weapon burnproof without sockets (or cursed for that matter). I'll leave it to you to work out how ;-)
That's whats I meant - it's possible to make any weapon or shield burnproofed without using sockets, thus why the argument "we don't need the message implenented as you should know your EQ" doesn't stand - you don't know WHAT is burnproofed or not. 
Dey
I also cast my vote in support of Dey's idea.
Go Dey!