Xdgmime implementation problem (text/plain)

[DaveMDS]

Hi, I need some help on the use of the f.d.o. xdgmime implementation:

xdgmime don't recognize text/plain file such as TODO files or any other 
unknow text file
(it recognize file like Makefile, AUTORS, README).
In other word any generic text file will be of type 
'application/octet-stream' instead of 'text/plain'
Is it normal?
it's a shared-mime-info problem?
Should I have to check manually the content of the file?

Thanks a lot.
Dave Andreoli