I installed Ubuntu 12.04, with texlive-full and texworks. When I double-click a .tex file in Nautilus, it pops up a

Do you want to run "xxxxxxxx.tex", or display it contents?

"xxxxxxxx.tex" is an executable text file.

Run in Terminal     Display       Cancel        Run

If I choose Display, it opens texworks. How can I make it open without seeing the above conversation window?

By the way, is .tex file indeed an executable file?

ADDED Just for the case, my ~/.local/share/applications/mimeapps.list file looks like the following:

[Default Applications]
text/html=google-chrome.desktop
x-scheme-handler/http=google-chrome.desktop
x-scheme-handler/https=google-chrome.desktop
x-scheme-handler/about=google-chrome.desktop
x-scheme-handler/unknown=google-chrome.desktop
text/x-tex=texworks.desktop
x-scheme-handler/mailto=google-chrome.desktop

[Added Associations]
text/x-tex=texworks.desktop;
text/x-bibtex=jabref.desktop;gedit.desktop;

I observe texworks are both up and down. Should I remove one?

ADDED

This does not happen with all .tex files. In fact, I am currently using Ubuntu 12.04 under Virtual Box with Windows 7 host. I have my Dropbox account synced with the Windows 7 host, and I access files in Dropbox in Ubuntu through Virtual Box's shared folder functionality. (I didn't install Dropbox client in Ubuntu.)

Files in Dropbox are owned by root with group vboxsf. My personal account is in the group vboxsf.

It seems that I have to uncheck the option for "executable", but I have all my .tex files in the Dropbox shared folder. Would there be any workaround?