I took your initial snippet of html and added it the and it added it to the Item Description section of a new listing
ensuring when I pasted the html I was in the "Source" view in the editor by clicking the Source button. When i previewed the item using the auctiva preview button I see
Which matches your image of what it's supposed to look like. If you are entering raw html in the Item Description with the "Source" button depressed, unclicking the "Source" button is not an actual preview of what your item description will look like on ebay. The editor control itself has styling being applied to it as a part of the overall lister page. i.e. html styling used by the Auctiva lister page is being applied to the editor in non-source mode, that won't be applied when the item description is rendered on ebay.
When using the source view of the editor, the html is appropriately rendered in the preview page (button at the bottom of the lister page) so you should be good to go.