If it's working in some cases and not others, then it may simply be coincidental. that those two have a problem. I did look at the code, and it seemed the end of the description section looked a little odd (and I saw the music player embed). The only thing that honestly concerns me is, code that isn't normally allowed could cause problems with any parsing their system does for whatever reason (including end-of-listing).
It would be best to consider modification of all your templates to remove those unaccepted headers and use the CSS method for background. I was hoping that could be done in tandem with the redesign (if any) for the new eBay listing page layout.
I don't mean to ramble; I just hate to have you start making changes only to restart the effort again in a few months. Coder time is MONEY. I just don't have enough evidence that the code is the cause of the status problem.
However, I do think Auctiva needs to tighten-up on the code allowed by the template editor. That's needed to prevent these drop-out problems and to meet the new safe-code design initiative.
CHANGE IS PAINFUL!