user.logout() from Flex don't log out

I'm trying to login/add content/logout from a Flex app. Eveything works fine except when I try to log out.
Flex responder object holds "true", but I'm still logged as the user I set in user.login().

One thing : in Drupal logs, line about opening session reports correct user name.
But the one about closing session holds "em" html tag for user name. No error reporting by the way.
It looks like this actually : http://drupal.org/node/411098

Don't know where the "em" tag come from. If I try "user.logout" from Services link in admin, it works ...