A Bing Help thread has a solo report of an issue with Bing leaving new sitemaps in the “pending” status.
Sitemaps can be submitted to Bing via their Webmaster Tools interface. The issue is, if you recently submitted a sitemap file, it may just be sitting in “pending” status.
Will from Bing confirmed the issue saying:
It is hard to tell how far back the issue goes but there is an older thread on this topic from early July.
Forum discussion at Bing Help.
