We just did a nice findout.
Ko has actually done something bad/good well it's up to you to decide, but they put upgradelimit on quest weapons.
all weapons that comes form Burning skeleton quest or the cleaver quest has a upgrade limit.
all burning skeleton weapons can get to +8.
and all cleaver quest weapons can get to +9.
some of a my friends had problems with upgradeing cause they wanted for example to do cleaver +10 and i wanted to do md +9.
it turned out that a few md's was upgradeable and a few wasn't. same with md and when we looked closer into it we found this.
i hope this helps u all.
to know if a weapon is quest or old u can see in the text under the weapon. On a md forexample: if it's a long text it can only get to +8 if it's a short text it can goes to rev 30