WebOb middleware call pattern discrepancy

middleware.py

from __future__ import print_function

from webob import Request
from webob.dec import wsgify

@wsgify.middleware
def add_magic_header(req, app, value='wibble'):
    resp = req.get_response(app)
    resp.headers['Magic-Header'] = value
    return resp

def nop(environ, start_response):
    start_response('200 OK', [('Content-Type', 'text/plain')])
    return ['OK']


req = Request.blank('/')
app = add_magic_header(nop, value='ELEPHANTS!')

resp1 = req.get_response(app)
resp2 = app(req)

print("resp1.headers['Magic-Header'] = %r" % resp1.headers['Magic-Header'])
print("resp2.headers['Magic-Header'] = %r" % resp2.headers['Magic-Header'])