I am not sure if this glitch is related to this ongoing problem but it came at the same time as the item specific issue arose and it seems (so far) to be limited to the clothing section.
A few sellers other than myself are suddenly finding some listings that we only have 1 item...suddenly has an available quantity of 6 for sale...6 seems to be the number for others as well.
Never used the quantity area since 1 is the default number.
It is a scary thing to think that I suddenly sold 3, 4 or 5 of an item that I only had a qty of 1.