It's widely accepted to extend formats with X-, so a line in a .document file with X- shouldn't cause a warning. Here's a simple patch.
Created attachment 19971 [details] [review] patch
Of course, it doesn't compile because I forgot an argument for strncmp, but it's trivial :-)
Use of freedesktop.org services, including Bugzilla, is subject to our Code of Conduct. How we collect and use information is described in our Privacy Policy.