Hello,
Thanks again Maxim ! With your help I've discovered that the bots which were redirected with a 301 weren't coming from my main domain (something.fr) but they were coming from another domain I have (something.com).
I had just setup the .com to redirect to the .fr but I weren't using it. Anyway, somehow some bots were visiting it... I'll fix this redirection problem in my configuration file so it won't happen anymore.
Olivier