The mkinitrd script does not honour the --fstab option.  I have appended a
patch.  Here
is the offending ouput with 'set -x':

# mkbootdisk --verbose --mkinitrdargs --fstab=/tmp/fstab 2.2.16-3
 .....
 + grep ^/dev/md --fstab=/tmp/fstab
  grep: unrecognized option `--fstab=/tmp/fstab'
  Usage: grep [OPTION]... PATTERN [FILE]...
  Try `grep --help' for more information.

# rpm -qf /sbin/mkinitrd
mkinitrd-2.4.1-2 

--- mkinitrd    Tue Feb 29 22:10:14 2000
+++ mkinitrd.new        Wed Aug 30 15:15:07 2000
@@ -96,7 +96,7 @@
     case $1 in
        --fstab*)
            if echo $1 | grep '=' >/dev/null ; then
-               fstab=`echo $1 | sed 's/^--with=//'`
+               fstab=`echo $1 | sed 's/^--fstab=//'`
            else
                fstab=$2
                shift