Let's assume that we have a LDAP group named Project_Builders, and Jenkins ACLs are configured for Project_builders.
Once saved, the configuration shows that the group has been found (group icon).
But people from the group cannot connect.Once the name is entered with the exact character's case, people can connect.

As far as the LDAP based ACL control is case sensitive, the LDAP search should also be case sensitive. So, in such a situation, the icon should have been the error icon.