Such a disconnect issue can be caused by the following situation - the item of the slot you've purchased visually in the client differs from the item on the slot in the database.
I've tried that earlier, if you return a different item than the one you've purchased in the client you are thrown out by a disconnect.
You should check your shop-tables for duplicated entries or messed up records in general - also you should extract the shop textfiles for the client from the database, just to be sure