Quantity throws an unrelated warning when converting through equivalencies?

I just noticed this one:

    >>> x = 50.*u.THz
    >>> x.to(u.eV, equivalencies=u.spectral())
    WARNING: Converting Quantity object in units 'J s' to a Numpy array [astropy.units.quantity]
    <Quantity 0.206783375651 eV>

It seems to get the conversion right, but it looks like the issue is deep in the units code for converting with equivalencies -- it looks like somewhere `_si.h` is getting converted into an array, but I don't see where (from a quick dig through the code). Maybe @mdboom knows where this could be?