Description of problem:
# LANG=C yum --installroot=/mnt/root distro-sync full
Loaded plugins: langpacks, presto, refresh-packagekit
Setting up Distribution Synchronization Process
Traceback (most recent call last):
  File "/usr/bin/yum", line 29, in <module>
    yummain.user_main(sys.argv[1:], exit_code=True)
  File "/usr/share/yum-cli/yummain.py", line 309, in user_main
    errcode = main(args)
  File "/usr/share/yum-cli/yummain.py", line 140, in main
    result, resultmsgs = base.doCommands()
  File "/usr/share/yum-cli/cli.py", line 462, in doCommands
    return self.yum_cli_commands[self.basecmd].doCommand(self, self.basecmd, self.extcmds)
  File "/usr/share/yum-cli/yumcommands.py", line 462, in doCommand
    return base.distroSyncPkgs(extcmds)
  File "/usr/share/yum-cli/cli.py", line 914, in distroSyncPkgs
    if found:
UnboundLocalError: local variable 'found' referenced before assignment

Version-Release number of selected component (if applicable):
# rpm -q yum
yum-3.4.3-5.fc16.noarch

From Fedora 16 Live.

How reproducible:
Always.