login trouble with django (is_autheticated switch from False to True each time page is refresh)

Hi everyone,
I have a wierd trouble when puting my app in production. In fact, the is_authenticated test from django change from True to False each time I refresh the page.
You can see the problem on my website TechLowPole, you just have to connect with user : test password : test. You will then be back on the home page, when you refresh this page (or any other one), you will loose or gain your authentification (as you can see at the top left corner with the name “test” and his address witch are displayed or not).
In my template, I use the {% if user.is_authenticated %} quote to change the informations there.
Thanks for your help.