Mobile Tools + Switchtheme : NO MORE REDIRECT

I work with :
Drupal 6.10 + Browscap 6.x-1.0 + Mobile Tools 6.x-1.0-rc1 + Switchtheme 6.x-1.0

Few weeks ago, everything was working well:
with a PC, I could login and see a default theme
with a mobile, I could see a dedicated theme

From my PC, everything is still OK.

Now, I am not able to login with the mobile:
I see the right login page, but I have the error message (from the mobile browser): "impossible to redirect"

If possible, I would prefer not to upgrade the modules...
Is this a problem from the Switchtheme module ?
What could I test ?

Thanks

ps: if I simulate a mobile from my PC (simulating the user agent), the redirection is OK: everything works well.