Operating System: Lubuntu 12.10
I create a small file using markdown syntax and save it as zxc.mkd. I have ReText 3.1.4 installed. I expect that double-clicking on the file in PCManFM should open the file with ReText. Instead it opens with Leafpad because the file description is "plain text document" (upper panel in image).
This does not happen in other file managers such as Thunar in which double-clicking properly opens the file in ReText because the file is seen as "Markdown document" (lower panel in image).