Tests using Django-1.6 fail

after installing Django-1.6, while Django-1.5 works flawless:

[mrunge@sofja horizon (master)]$ ./run_tests.sh -N
Running Horizon application tests
Traceback (most recent call last):
  File "/home/mrunge/work/horizon/manage.py", line 23, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/lib/python2.7/site-packages/django/core/management/__init__.py", line 399, in execute_from_command_line
    utility.execute()
  File "/usr/lib/python2.7/site-packages/django/core/management/__init__.py", line 392, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/lib/python2.7/site-packages/django/core/management/commands/test.py", line 50, in run_from_argv
    super(Command, self).run_from_argv(argv)
  File "/usr/lib/python2.7/site-packages/django/core/management/base.py", line 238, in run_from_argv
    parser = self.create_parser(argv[0], argv[1])
  File "/usr/lib/python2.7/site-packages/django/core/management/commands/test.py", line 59, in create_parser
    option_list=options)
  File "/usr/lib64/python2.7/optparse.py", line 1219, in __init__
    add_help=add_help_option)
  File "/usr/lib64/python2.7/optparse.py", line 1261, in _populate_option_list
    self.add_options(option_list)
  File "/usr/lib64/python2.7/optparse.py", line 1039, in add_options
    self.add_option(option)
  File "/usr/lib64/python2.7/optparse.py", line 1020, in add_option
    self._check_conflict(option)
  File "/usr/lib64/python2.7/optparse.py", line 995, in _check_conflict
    option)
optparse.OptionConflictError: option -p/--pattern: conflicting option string(s): -p