Intransitive behavior in calculating separation of alt-az coordinates #5650

In [1]: from astropy.time import Time
   ...: from astropy import coordinates as coord, units as u
   ...: from astropy.coordinates.tests.utils import randomly_sample_sphere
   ...: times = Time.now() + np.linspace(0,10,12)*u.day
   ...: lapalma = coord.EarthLocation.of_site('lapalma')
   ...: frame = coord.AltAz(obstime=times, location=lapalma)
   ...: moon = coord.get_moon(times)
   ...: coos = coord.SkyCoord(*(
   ...:     np.reshape(_, (-1, 1)) for _ in randomly_sample_sphere(3)))
   ...: altaz = coos.transform_to(frame)
   ...: moon_altaz = moon.transform_to(frame)
   ...: altaz.separation(moon_altaz) # this works
   ...: 
Out[1]: 
<Angle [[ 139.0388979 , 138.23843479, 135.06332784, 129.70181874,
          122.73431463, 114.85028243, 106.5549471 ,  98.05920802,
           89.34874134,  80.34706644,  71.1096006 ,  61.99276037],
        [  51.46208807,  61.70674564,  72.57274178,  83.92909374,
           95.47107488, 106.87666585, 117.98115975, 128.83409021,
          139.59927098, 150.28646499, 160.0375782 , 164.83114461],
        [  43.8953635 ,  52.06206336,  61.28994984,  71.29723246,
           81.68591216,  92.06381851, 102.20185075, 112.0833638 ,
          121.80899218, 131.38692475, 140.40763961, 147.5993305 ]] deg>

In [2]: moon_altaz.separation(altaz) # this raises an exception
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-2-5447e2eaa179> in <module>()
----> 1 moon_altaz.separation(altaz)

/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/astropy/coordinates/sky_coordinate.pyc in separation(self, other)
    676 
    677         if isinstance(other, SkyCoord):
--> 678             self_in_other_system = self.transform_to(other.frame)
    679         elif isinstance(other, BaseCoordinateFrame) and other.has_data:
    680             # it's a frame

/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/astropy/coordinates/sky_coordinate.pyc in transform_to(self, frame)
    437         # Do the transformation, returning a coordinate frame of the desired
    438         # final type (not generic).
--> 439         new_coord = trans(self.frame, generic_frame)
    440 
    441         # Finally make the new SkyCoord object from the `new_coord` and

/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/astropy/coordinates/transformations.pyc in __call__(self, fromcoord, toframe)
    905 
    906             curr_toframe = t.tosys(**frattrs)
--> 907             curr_coord = t(curr_coord, curr_toframe)
    908 
    909         # this is safe even in the case where self.transforms is empty, because

/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/astropy/coordinates/transformations.pyc in __call__(self, fromcoord, toframe)
    705 
    706     def __call__(self, fromcoord, toframe):
--> 707         res = self.func(fromcoord, toframe)
    708         if not isinstance(res, self.tosys):
    709             raise TypeError('the transformation function yielded {0} but '

/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/astropy/coordinates/builtin_frames/cirs_observed_transforms.pyc in altaz_to_altaz(from_coo, to_frame)
    131     # for now we just implement this through CIRS to make sure we get everything
    132     # covered
--> 133     return from_coo.transform_to(CIRS(obstime=from_coo.obstime)).transform_to(to_frame)

/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/astropy/coordinates/baseframe.pyc in transform_to(self, new_frame)
    986             msg = 'Cannot transform from {0} to {1}'
    987             raise ConvertError(msg.format(self.__class__, new_frame.__class__))
--> 988         return trans(self, new_frame)
    989 
    990     def is_transformable_to(self, new_frame):

/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/astropy/coordinates/transformations.pyc in __call__(self, fromcoord, toframe)
    905 
    906             curr_toframe = t.tosys(**frattrs)
--> 907             curr_coord = t(curr_coord, curr_toframe)
    908 
    909         # this is safe even in the case where self.transforms is empty, because

/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/astropy/coordinates/transformations.pyc in __call__(self, fromcoord, toframe)
    705 
    706     def __call__(self, fromcoord, toframe):
--> 707         res = self.func(fromcoord, toframe)
    708         if not isinstance(res, self.tosys):
    709             raise TypeError('the transformation function yielded {0} but '

/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/astropy/coordinates/builtin_frames/cirs_observed_transforms.pyc in cirs_to_altaz(cirs_coo, altaz_frame)
     81                                       distance=distance,
     82                                       copy=False)
---> 83     return altaz_frame.realize_frame(rep)
     84 
     85 

/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/astropy/coordinates/baseframe.pyc in realize_frame(self, representation)
    876                         for attr in self.get_frame_attr_names()
    877                         if attr not in self._attr_names_with_defaults])
--> 878         return self.__class__(representation, **frattrs)
    879 
    880     def represent_as(self, new_representation, in_frame_units=False):

/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/astropy/coordinates/builtin_frames/altaz.pyc in __init__(self, *args, **kwargs)
     94 
     95     def __init__(self, *args, **kwargs):
---> 96         super(AltAz, self).__init__(*args, **kwargs)
     97 
     98     @property

/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/astropy/coordinates/baseframe.pyc in __init__(self, *args, **kwargs)
    660                 # Validate attribute by getting it.  If the instance has data,
    661                 # this also checks its shape is OK.  If not, we do it below.
--> 662                 values[fnm] = getattr(self, fnm)
    663             else:
    664                 setattr(self, '_' + fnm, fdefault)

/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/astropy/coordinates/baseframe.pyc in __get__(self, instance, frame_cls)
    233                         "attribute {0} should be scalar or have shape {1}, "
    234                         "but is has shape {2} and could not be broadcast."
--> 235                         .format(self.name, instance_shape, out.shape))
    236 
    237                 converted = True

ValueError: attribute obstime should be scalar or have shape (12,), but is has shape (3, 12) and could not be broadcast.