Quantity displayed on sold items

[Argh]

After selling an item to a merchant that the merchant is not already selling (ie. Clamcakes sold to Terman Underbelly) the quantity of that item that the vendor now has is always displayed wrong. It does not change from this number as the quantity increases or decreases.

This number appears different on different merchants:

If I sell one clamcake to Terman Underbelly it appears as though he is selling thirteen clamcakes.

If I sell one clamcake to Dalgrim Underbelly it appears as though he is selling five clamcakes.

If I sell one clamcake to Caitlin Underbelly it appears as though she is selling six clamcakes.