Try editing the following files.
/home/yourusername/.local/share/applications/mimeapps.list
You can assign the default applications here.
Alternatively, you could also edit
/home/yourusername/.local/share/applications/defaults.list
-or-
/usr/share/applications/defaults.list.
I believe, if you edit the /usr/share ... it will change the default associations for all users while the one in your home folder will change only for you. I do not know why the same file or smaller versions of the file in /usr/share/... is found in home folder.
Hope this helps.
---------- Post added at 09:46 AM ---------- Previous post was at 09:46 AM ----------
EDIT:
Looking at your problem, I think you might have to edit the file under /usr/share ...
---------- Post added at 09:56 AM ---------- Previous post was at 09:46 AM ----------
Further edit:
Sorry for multiple edits ... Perhaps, this is what you might need to add
Code:
application/rtf=wine-extension-rtf.desktop