I have had this problem MANY times. In fact, I am having it right now and that's why I'm reading the forum at this time. It is what drove me away from Auctiva in the past and I've only recently come back hoping the issue was resolved. I mainly use Firefox but even when switching from Firefox to IE I still have the issue. At this time only half of my listing is being saved, yes that is half of ONE listing not half of the listings I try and create. I am quite frustrated with this issue. If there is any advice I can give (and unfortunately it is minimal and very hit and miss); since I create my listings in an external editor i.e. Frontpage or Dreamweaver, I have had some sporadic luck by entering into Auctiva's HTML mode and entering a character i.e. a space or a period at the beginning of my listing and THEN pasting my HTML into the form and then once again entering another character into the form prior to saving it. I hope that makes some semblance of sense because I tend to even confuse myself at times
Anyway, give it a try and again, it is hit and miss. Also, you can (and I have in the past) enter in your HTML and immediately post the listing to ebay before you save it. You can then use the relist feature once that listing ends.
Hope that helps some...