With mkinitrd-5.1.19.6-61.el5_5.2 and /etc/multipath.conf looking like:

defaults {
        user_friendly_names yes
        bindings_file /etc/multipath/bindings
}

The resulting initrd.img  contains the correct bindings file:

# zcat test.img | cpio -t | grep multi
30204 blocks
bin/multipath
etc/multipath
etc/multipath/bindings
etc/multipath.conf

NOTE: The "=" character ( as in bindings_file = ... ) from https://bugzilla.redhat.com/show_bug.cgi?id=593050#c0 is incorrect syntax. All example conf files from the device-mapper-multipath package show "bindings_file /path/to/file" syntax.


Moving to VERIFIED.

An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on therefore solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.

http://rhn.redhat.com/errata/RHBA-2010-0541.html