Currently, any subsequent updates of an RSS feeds sent from Calibre to Kindle *on the same day* suffer by the problem of displaying/sorting incorrectly in Kindle:
Currently, the news sent from Calibre are marked as periodicals (called "issues" in Kindle). However, the default behaviour for standard ebooks (called "documents" in Kindle) or blogs should fix this problem: the latest issue would simply replace the previous one in Kindle, without the feature of saving "older" issues as is the case with periodicals which is broken for updates on the same day.
So my question is: How can I set the type of the document for Kindle in Calibre? I could not find it either in the metadata or in the html. And is it possible to change the type for the news delivered automatically by Calibre?