I had an odd problem with an article today... when I tried to navigate to it using a local link, instead of displaying the article, I got the dialog "Unknown file type" with options to open or save.
Trying the shotgun approach, I navigated to the article by typing the URL in the address window of the browser. I was able to see the article. I clicked the "edit" tab and saved it without changing. The problem then went away.
Does anyone know what happened?