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.

In Drupal logs, line about opening session reports correct user name.
But the one about closing session holds "em" tag for user name.
No error by the way.

If I try "user.logout" from Services link in admin, it works. Any idea ?