astropy.io.fits.fitsrec:FITS_rec.copy

Summary

The Numpy documentation lies; numpy.ndarray.copy is not equivalent to numpy.copy. Differences include that it re-views the copied array as self's ndarray subclass, as though it were taking a slice; this means __array_finalize__ is called and the copy shares all the array attributes (including ._converted!). So we need to make a deep copy of all those attributes so that the two arrays truly do not share any data.