In anaconda-11.2.0.40-2, when the "Add additional software repositories button" is clicked, anaconda always tries to fetch a dhcp address, whether the network interface is configured or not. (see bug #232512). Even if the device is not configured, the installer then hangs forever while waiting for a dhcp response. There should probably be a timeout on waiting for that response.
*** This bug has been marked as a duplicate of 232512 ***