Setting default multicast settings does not propagate to the cluster.conf file and there are no defaults set in the "Network Configuration" page for multicast.
This has been fixed (and the experimental broadcast option has been disabled) in commit 33185dbcf43f6889478bcf3012ce487c9d68f7a2
This request was evaluated by Red Hat Product Management for inclusion in a Red
Hat Enterprise Linux major release. Product Management has requested further
review of this request by Red Hat Engineering, for potential inclusion in a Red
Hat Enterprise Linux Major release. This request is not yet committed for
Red Hat Enterprise Linux 6.0 is now available and should resolve
the problem described in this bug report. This report is therefore being closed
with a resolution of CURRENTRELEASE. You may reopen this bug report if the
solution does not work for you.