In my libsmbios project, I had changed the %description to "%description -n libsmbios_c" and osc updatepacmetafromspec fails with:

$ osc updatepacmetafromspec
Traceback (most recent call last):
  File "/usr/bin/osc", line 12, in <module>
    r = babysitter.run(osccli)
  File "/usr/lib/python2.5/site-packages/osc/babysitter.py", line 40, in run
    return prg.main()
  File "/usr/lib/python2.5/site-packages/osc/cmdln.py", line 256, in main
    return self.cmd(args)
  File "/usr/lib/python2.5/site-packages/osc/cmdln.py", line 279, in cmd
    retval = self.onecmd(argv)
  File "/usr/lib/python2.5/site-packages/osc/cmdln.py", line 395, in onecmd
    return self._dispatch_cmd(handler, argv)
  File "/usr/lib/python2.5/site-packages/osc/cmdln.py", line 1070, in _dispatch_cmd
    return handler(argv[0], opts, *args)
  File "/usr/lib/python2.5/site-packages/osc/commandline.py", line 913, in do_updatepacmetafromspec
    p.read_meta_from_spec(specfile)
  File "/usr/lib/python2.5/site-packages/osc/core.py", line 1051, in read_meta_from_spec
    data = read_meta_from_spec(specfile, 'Summary', 'Url', '%description')
  File "/usr/lib/python2.5/site-packages/osc/core.py", line 1865, in read_meta_from_spec
    start = lines.index(m.group()) + 1
ValueError: list.index(x): x not in list

I had changed the %description because there are several sub-RPMs built from one spec and it was convenient to keep them all separate if they each had the package name in the section name.