Cannot add beam when setting north=True

[astrojysun]

I got the following error when working on an image that has beam information in its header:

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
/var/folders/qh/btyjv_d12px7hzhdnhx71t8m0000gn/T/ipykernel_66057/151975569.py in <module>
     37     ra_deg, dec_deg, width=width_deg, height=height_deg)
     38 subfig.show_colorscale(cmap='coolwarm')
---> 39 subfig.add_beam()
     40 subfig.beam.set_facecolor('w')
     41 subfig.beam.set_linewidth(0)

~/software/miniconda3/envs/py3.7/lib/python3.7/site-packages/aplpy/decorators.py in wrapper(*args, **kwargs)
     26 
     27         try:
---> 28             return f(*args, **kwargs)
     29         finally:
     30             mydata.nesting -= 1

~/software/miniconda3/envs/py3.7/lib/python3.7/site-packages/aplpy/core.py in add_beam(self, *args, **kwargs)
   1970         # Initalize the beam and set parameters
   1971         b = Beam(self)
-> 1972         b.show(*args, **kwargs)
   1973 
   1974         if hasattr(self, 'beam'):

~/software/miniconda3/envs/py3.7/lib/python3.7/site-packages/aplpy/decorators.py in wrapper(*args, **kwargs)
     26 
     27         try:
---> 28             return f(*args, **kwargs)
     29         finally:
     30             mydata.nesting -= 1

~/software/miniconda3/envs/py3.7/lib/python3.7/site-packages/aplpy/overlays.py in show(self, major, minor, angle, corner, frame, borderpad, pad, **kwargs)
    379 
    380         if isinstance(major, str):
--> 381             major = self._header[major]
    382 
    383         if isinstance(minor, str):

~/software/miniconda3/envs/py3.7/lib/python3.7/site-packages/astropy/io/fits/header.py in __getitem__(self, key)
    155             keyword = key
    156 
--> 157         card = self._cards[self._cardindex(key)]
    158 
    159         if card.field_specifier is not None and keyword == card.rawkeyword:

~/software/miniconda3/envs/py3.7/lib/python3.7/site-packages/astropy/io/fits/header.py in _cardindex(self, key)
   1744 
   1745         if not indices:
-> 1746             raise KeyError(f"Keyword {keyword!r} not found.")
   1747 
   1748         try:

KeyError: "Keyword 'BMAJ' not found."

Upon further tests, I noticed this error would go away if I don't use north=True when initializing the FITSFigure object. I haven't checked the source code, but I am guessing that the header information somehow gets dropped when converting the header to make the image north-aligned?