sitemap limited to 80000 urls in Google Webmaster Admin page

I have published my forum's sitemap which have more than 100000 urls separated in several files like :
sitemap_1.xml.gz, sitemap_2.xml.gz, ..., sitemap_10.xml.gz (each file has 10000 urls).
But i have noticed since several months that this sitemap is limited only to 80000 urls in Google's side. In the Google's webmaster admin tool, i can see only files from sitemap_1.xml.gz to sitemap_8.xml.gz.

Do you have any idea ?

i recommend 30k per file, and not including non-important items.

see my ultiamte guide (link in sig) for a screen shot of my recommended sitemap settings.