All pages dropped after adding sitemap

Yahoo had onlu indexed about 86 of my 400+ pages so in an effort to improve this I added a yahoo sitemap to my site about 2 weeks ago. I submitted it to:

[link] and followed all the guidelines. I named it urllist.txt and put it on my server. All seemed to go well though yahoo offers no confirmation message.

The very next day all of my 86 pages that I had indexed on Yahoo were gone. Only my homepage at www.mysite.com and 1 product page which linked to a product that was no longer available were listed.

Is this due to the sitemap submission? I have had no new yahoo pages listed since this occurred. Also Yahoo is indexing pages on my site at about 1 a day with session ID's (though they are indexing pages at a greater rate than this overall and most without session ID's). I have session ID's diabled for search engine spiders and no other search engine spider does this. This did not occur before the sitemap submission but is probably coincidental.

Any help would be most appreciated.

Very strange, my pages returned last night only hours after posting this. There is at least as many pages as there was before I added the sitemap. What is odd is there is now some really old pages that are not even on my current site, they are from a previous version of the site I wrote 5 months ago. All of these pages return a 404 error, I wonder if Yahoo will spider them and realize this.