Strange behavior after upgrading to 2.7.x

[vittore]

After a minor upgrading I get a strange behavior.
If ldap user is into Domain admins (Microsoft Active directory) all go right: user authenticated with no problem.
If ldap user is not into Domain admins (Microsoft Active directory) there is an infinite loop. Logs say no fully authenticated. User not found.

Any ideas?

Thanks in advance.
v.