For certain text files, I get the following error message when I click on them
in Nautilus 2.14.1:

<error>
Cannot open test.txt

The filename "test.txt" indicates that this file is of type "txt document". The
contents of the file indicate that the file is of type "plain text document". If
you open this file, the file might present a security risk to your system.

Do not open the file unless you created the file yourself, or received the file
from a trusted source. To open the file, rename the file to the correct
extension for "plain text document", then open the file normally. Alternatively,
use the Open With menu to choose a specific application for the file. 
</error>

I can only presume this is a bug, since I'm unaware of any real distinction
between "txt document" and "plain text document".

I haven't been able to narrow down what specific content causes this confusion
but I've been able to reproduce this problem using the attached file. The name
of the file doesn't seem to make any difference.