I went through several of your listings that appeared to be missing a background, and did confirm that those HTML codes are indeed removed. I have a new piece of code that I'd recommend you test and see if the eBay editor will accept and possibly restore backgrounds (fix the broken ones).
Here's the code, which you insert at the beginning of the Description with the edtior in HTML mode:
background: url("http://i237.photobucket.com/albums/ff42/SamHiland1/edit.jpg") fixed;
You may need to retype this code, as copy and paste from the Forum will add extraneous text.
Just subtitute the link inside the " " for whichever background is missing. This code is essentially equivalent to that code that's removed. It uses CSS Style coding, which appears to be acceptable to eBay and Auctiva from some of my tests. Note, I used the attribute "fixed" to make sure the background doesn't move with the scrollbar.
When you test, just insert the code and use the Revise listing PREVIEW to see if it's working. If this fix holds, I'll pass you updated code for the template.
Edit: I stored the code at practiceboard to make it easier to copy.