Thanks for posting about your experience here.
I have not heard of the specific behavior you described before but, given that the listing categories changed *after* the items in question were submitted to eBay, I do not see how this could be a result of anything on the Auctiva side of things.
However, I have seen eBay redirect items to different categories than were selected during the listing process based on the provided UPC details on occasion, so perhaps they have a similar process in place to automatically move active listings to different categories when they meet certain conditions.
In any event, I believe that continuing to pursue this through eBay's Customer Support team is the proper course of action here. Hopefully they will be able to get to the bottom of this and provide you with an explanation soon.