Why try to update (some) permissions which are the same?

[Perry Hutchison]

On the source system:

$ rsync --version
rsync  version 2.6.8  protocol version 29
Copyright (C) 1996-2006 by Andrew Tridgell, Wayne Davison, and others.
<http://rsync.samba.org/>
Capabilities: 64-bit files, socketpairs, hard links, ACLs, symlinks, batchfiles,
              inplace, IPv6, file flags, 32-bit system inums, 64-bit internal inums
...

$ ll -d fcst-200[89] fcst-201[01]
dr-xr-xr-x  2 perryh  perryh  7168 Nov 27  2009 fcst-2008
dr-xr-xr-x  2 perryh  perryh  9216 Jul 21  2010 fcst-2009
drwxr-xr-x  2 perryh  perryh  9216 Jul  7  2011 fcst-2010
drwxr-xr-x  2 perryh  perryh  4608 Jul  7  2011 fcst-2011

$ rsync -uHSxz4rlptOgv --itemize-changes -e rsh fcst-200[89] fcst-201[01] fbsd81:/home/perryh
building file list ... done
rsync: failed to modify permissions on "/home/perryh/fcst-2008": Operation not permitted (1)
rsync: failed to modify permissions on "/home/perryh/fcst-2009": Operation not permitted (1)

sent 15794 bytes  received 20 bytes  31628.00 bytes/sec
total size is 278224  speedup is 17.59
rsync error: some files could not be transferred (code 23) at main.c(892) [sender=2.6.8]


On the destination system:

$ ll -d fcst-200[89] fcst-201[01]
dr-xr-xr-x  2 perryh  perryh  uchg,uunlnk 7168 Nov 27  2009 fcst-2008
dr-xr-xr-x  2 perryh  perryh  uchg,uunlnk 9216 Jul 21  2010 fcst-2009
drwxr-xr-x  2 perryh  perryh  uchg,uunlnk 9216 Jul  7  2011 fcst-2010
drwxr-xr-x  2 perryh  perryh  uchg,uunlnk 4608 Jul  7  2011 fcst-2011

$ rsync --version
rsync  version 3.0.7  protocol version 30
Copyright (C) 1996-2009 by Andrew Tridgell, Wayne Davison, and others.
Web site: http://rsync.samba.org/
Capabilities:
    64-bit files, 32-bit inums, 32-bit timestamps, 64-bit long ints,
    socketpairs, hardlinks, symlinks, IPv6, batchfiles, inplace,
    append, ACLs, xattrs, no iconv, symtimes
...


The question is:  why does rsync attempt (and fail) to change the
permissions of two destination directories, and not the other two,
when the permissions of all four destination directories already
match the corresponding source directories?  (The change attempt
fails because of the destinations' uchg,uunlnk flags, but as far
as I can see the change should never have been attempted in the
first place.)