I tried running authconfig manually after the installer had completed in order to enable LDAP authentication. No luck -- in fact, I noticed that the ldap.conf in /etc (which is used by the pam_ldap and nss_ldap modules) contained no 'host' or 'base' directives at all.
That's odd. Commenting them out on my test machine and entering new values in the dialog causes new host and base directives to be appended. Do you have an existing configuration file that for some reason you wouldn't be able to read? Or are you somehow managing to run it as a non-root user?
This is probably an artifact of bug 13157, which probably ate the entries during the install. However, it does point to a bug in authconfig as well, which ought to deal sanely when there are no existing (commented or otherwise) host or base entries in the config file.
Adding bogus entries: host foo base foo And re-running authconfig makes things work as expected.
I still can't reproduce this problem. Removing my ldap.conf file and running authconfig (in both interactive and kickstart modes) generates a correct file.