Curious rdiff-backup problem, two identical installs, only one works

[Stuart Robertson]

I have two macs, both running 10.7.2 and Macports 2.0.3, both
up-to-date. One Macports installation is six months old, the other
new. On the older installation rdiff-backup installs and runs, on the
new Macports installation rdiff-backup installs but fails to run with
the following error.

/opt/local/bin/rdiff-backup --version
Traceback (most recent call last):
 File "/opt/local/bin/rdiff-backup", line 20, in <module>
  import rdiff_backup.Main
 File "/opt/local/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/rdiff_backup/Main.py",
line 25, in <module>
  import Globals, Time, SetConnections, selection, robust, rpath, \
 File "/opt/local/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/rdiff_backup/SetConnections.py",
line 30, in <module>
  import Globals, connection, rpath
 File "/opt/local/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/rdiff_backup/connection.py",
line 539, in <module>
  import Globals, Time, Rdiff, Hardlink, FilenameMapping, C, Security, \
 File "/opt/local/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/rdiff_backup/Rdiff.py",
line 22, in <module>
  import os, librsync
 File "/opt/local/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/rdiff_backup/librsync.py",
line 28, in <module>
  import _librsync
ImportError: dlopen(/opt/local/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/rdiff_backup/_librsync.so,
2): Symbol not found: _rs_appendflush
 Referenced from: /opt/local/lib/librsync.1.dylib
 Expected in: flat namespace
in /opt/local/lib/librsync.1.dylib

I've looked at the installed ports and the active ports seem to be
exactly the same on each machine (I've pasted the list of installed
ports below). I've looked at /opt/local/lib/ on both machines and
files present are the same.

How do I find out what is preventing rdiff-backup running on the new install?

/Stuart

Working machine, ports installed

autoconf @2.68_2 (active)
 autoconf263 @2.63_0 (active)
 automake @1.11.1_0 (active)
 bzip2 @1.0.6_0 (active)
 cmake @2.8.6_0 (active)
 curl-ca-bundle @7.22.0_0
 curl-ca-bundle @7.22.0_1
 curl-ca-bundle @7.23.1_0 (active)
 db46 @4.6.21_6 (active)
 expat @2.0.1_1 (active)
 fuse4x @0.8.12_0
 fuse4x @0.8.13_0 (active)
 fuse4x-kext @0.8.12_0+universal
 fuse4x-kext @0.8.13_0+universal (active)
 gdbm @1.9.1_0
 gdbm @1.10_0 (active)
 gettext @0.18.1.1_2 (active)
 ghc @6.10.4_5 (active)
 glib2 @2.28.8_0
 glib2 @2.30.2_1 (active)
 gmp @5.0.2_1 (active)
 gperf @3.0.4_2 (active)
 help2man @1.40.4_1 (active)
 hs-binary @0.5.0.2_0 (active)
 hs-citeproc @0.3.1_1 (active)
 hs-digest @0.0.0.9_0 (active)
 hs-dlist @0.5_0 (active)
 hs-ghc-paths @0.1.0.6_0 (active)
 hs-haddock @2.5.0_1 (active)
 hs-HTTP @4000.1.1_0 (active)
 hs-json @0.4.4_0 (active)
 hs-pandoc-types @1.8_0 (active)
 hs-tagsoup @0.12_0 (active)
 hs-texmath @0.5_0 (active)
 hs-utf8-string @0.3.6_0 (active)
 hs-xml @1.3.7_0 (active)
 hs-zip-archive @0.1.1.7_0 (active)
 hs-zlib @0.5.2.0_0 (active)
 libedit @20110802-3.0_0 (active)
 libffi @3.0.10_2 (active)
 libiconv @1.14_0 (active)
 libidn @1.22_0 (active)
 librsync @0.9.7_1 (active)
 libtool @2.4.2_0 (active)
 m4 @1.4.16_0 (active)
 man2html @3.0.1_1 (active)
 mercurial @1.9.1_0
 mercurial @1.9.3_0
 mercurial @2.0_0 (active)
 ncurses @5.9_1 (active)
 ncursesw @5.8_0 (active)
 openssl @1.0.0e_1 (active)
 p5.12-locale-gettext @1.50.0_6 (active)
 pandoc @1.8.0.1_0 (active)
 perl5 @5.12.3_1+perl5_12 (active)
 perl5.8 @5.8.9_5 (active)
 perl5.12 @5.12.3_2 (active)
 pkgconfig @0.26_0 (active)
 py-cherrypy @2.3.0_1 (active)
 py26-distribute @0.6.24_0 (active)
 py26-xattr @0.6.1_0 (active)
 python24 @2.4.6_10 (active)
 python26 @2.6.7_1
 python26 @2.6.7_2
 python26 @2.6.7_3 (active)
 python27 @2.7.2_2
 python27 @2.7.2_3 (active)
 python_select @0.3_1 (active)
 rdiff-backup @1.2.8_2 (active)
 readline @6.2.000_0 (active)
 sqlite3 @3.7.8_1
 sqlite3 @3.7.9_0 (active)
 xz @5.0.3_0 (active)
 zlib @1.2.5_0 (active)

non-working install

autoconf @2.68_2 (active)
 automake @1.11.1_0 (active)
 bzip2 @1.0.6_0 (active)
 db46 @4.6.21_6 (active)
 expat @2.0.1_1 (active)
 fuse4x @0.8.13_0 (active)
 fuse4x-kext @0.8.13_0+universal (active)
 gdbm @1.10_0 (active)
 gettext @0.18.1.1_2 (active)
 glib2 @2.30.2_2 (active)
 gperf @3.0.4_2 (active)
 help2man @1.40.4_1 (active)
 libedit @20110802-3.0_0 (active)
 libffi @3.0.10_2 (active)
 libiconv @1.14_0 (active)
 librsync @0.9.7_1 (active)
 libtool @2.4.2_0 (active)
 m4 @1.4.16_0 (active)
 ncurses @5.9_1 (active)
 ncursesw @5.8_0 (active)
 openssl @1.0.0e_1 (active)
 p5.12-locale-gettext @1.50.0_6 (active)
 perl5 @5.12.3_1+perl5_12 (active)
 perl5.12 @5.12.3_2 (active)
 pkgconfig @0.26_1 (active)
 py-cherrypy @2.3.0_1 (active)
 py26-distribute @0.6.24_0 (active)
 py26-xattr @0.6.1_0 (active)
 python24 @2.4.6_10 (active)
 python26 @2.6.7_3 (active)
 python27 @2.7.2_3 (active)
 python_select @0.3_1 (active)
 rdiff-backup @1.2.8_2 (active)
 sqlite3 @3.7.9_0 (active)
 xz @5.0.3_0 (active)
 zlib @1.2.5_0 (active)