I took a look at this. Both use the equal ufunc. However, x==x goes through array_richcompare() first, and array_richcompare() has extra code that is recovering from the failure.

The end of array_richcompare() (arrayobject.c, line 1433):

    if (result == Py_NotImplemented) {
        /* Try to handle string comparisons */
        ...
    }
    return result;

So it appears that the underlying problem is that ufuncs do not work with flex arrays. For example,

>>> x = numpy.zeros(1, dtype='d,d')
>>> numpy.add(x, x)
NotImplemented

See also

#4470
#3322
#3015

Going to close this, while still true in some other cases, it isn't for strings since 1.25 or so.