I'm having the exact same problem that walrus described back in February: [webmasterworld.com...]
This started on July 2nd. Site Explorer complains about being unable to validate my site with the meta tag. Nothing has changed on my end. I just did a new authentication request through the YSE dashboard, which is currently pending.
Meanwhile, Yahoo completely stopped sending traffic on July 2nd and just a handful of visitors yesterday and today. This could be a coincidence: the site is currently ranking where I expect it (checked only after submitting the authentication request).
my site, about 17 pages, returns 358 pages - many urls with the main domain name in as www.example.com, so example, get returned.
I've seen SiteExplorer return a lot of urls with different tracking strings on them that otherwise all go to the same page... and count them all as separate pages.
There are ways to use mod_rewrite to eliminate these strings, but if you do you'll need to exclude ppc landing pages from your rewrites (or else you'll be rewriting ppc tracking urls and won't be able to collect stats with various analytics packages that use tracking strings and onpage tracking code).