Problem with NPC's

OK...here is one for all you NPC adding people on here....lol
when i put stones , elixers and other stackable items into a NPC if you buy more then 1 item at a time it will boot you out of the game , it will give you the items with no problems but it still boots you out , anyone know why or how to fix it ?

NOW...before you start with the maxstack crap YES the max stack is correct in refobjectitem both on the database and the client of 50 so you should be able to buy 50 at a time without crashing but it will not work and its driving me crazy
is there something that i am missing like a peramitor or NPC code like the item Mall stuff that only allows 5 items at 1 time or what ? Thanks for any help or info