In firstboot the LDAP config OK and Cancel buttons don't work, and the command-line version doesn't return from updating the base DN and server.
What authconfig version is it?
Can you strace the command-line version?
Oh sure, as soon as you look at the bug it starts behaving properly...
Well, the firstboot problem is real and will be fixed in next package version. So thank you for catching it. I cannot reproduce the command-line authconfig hang either so I'm afraid that I cannot fix this one.