It seems the other problem has been fixed as well, so thanks bingdude for the help!
The only problem is that some of the sitemaps I added in early July still has the "pending" status, but some have been processed already.
However, I noticed something that I'm not quite sure if it's intentional or not. I have the main site as www.example.com, and a forum on forum.example.com, which I added as a separate site in Bing Webmaster Center. But the sitemap I added for the forum appears under the main site's section as well. I've tried to remove it, but it just comes back.
I would prefer to have "www" separate from "forum" and other sub-domains, since otherwise the data gets confusing.