Here is the note we received from another MW user recently :
"I've done a little more trouble shooting on my end, and I've determined that the problem is with Marketworks. I use the pre-generated code from Vendio in my Marketworks auction templates... It seems that Marketworks implemented a change on 04-18-2006 that strips out most of the white space from that code during the listing process, which results in the non-functioning behavior on my most recently listed items."
Unfortunately the only workaround would be to opt for Vendio to insert the HTML code for the gallery automatically into your ads instead, so it appears after MW does not have control over the item description content.