ok, i have irritated so long that almost all stackable items
in wotlk didnt stack at all, like reagents, cloth, or heroism marks...

I first thought it was the items theyrself that was ****ed,

then i got the idea that maybe the vendors was wrong,
and i was right. If Amount field is 0 or -1 then it will never stack



Code:
update vendors set amount = 1 where amount = -1;
update vendors set amount = 1 where amount = 0;


Run this into your world database and ALL stackable items
will work again :P