Tested in Firefox 31.6.0 on English Wikipedia at https://en.wikipedia.org/wiki/User:Mattflaschen_%28WMF%29/Sandbox?veaction=edit:
- Blank the surface.
- Click link icon.
- Paste in File:BetaFeatures-Hovercards-Thumbnail-rtl.svg
- Click Insert button
- The link in the surface (not the context item) goes to https://en.wikipedia.org/%3AFile%3ABetaFeatures-Hovercards-Thumbnail-rtl.svg .
See T96492: Previewing a link to a File in Flow's VE-mode, opens a broken destination due to /w/