twisted: mixed @inlineCallbacks + Deferred

gistfile1.txt

from twisted.internet.defer import Deferred, inlineCallbacks, returnValue

d0 = Deferred()
d1 = Deferred()
d2 = Deferred()

@inlineCallbacks
def foo(arg):
    print 'foo', arg
    x = yield d1
    x = 'foo-' + str(x)
    print 'foo() is returning', x
    returnValue(x)

def quux(arg):
    print "quux", arg
    d = foo('blam')
    print 'quux() is returning', d
    return d

@inlineCallbacks
def bar(arg):
    print 'bar', arg
    z = yield quux(arg)
    print 'bar() is returning', z
    returnValue(z)

d2.callback('d2')
d1.callback('d1')
d0.addCallback(bar)

assert d2.result == 'd2'
assert d1.result == 'd1'
d0.callback('d0')

assert d2.result == 'd2'
assert d0.result == 'foo-d1'
# somehow, d1's result has become None here ...
assert d1.result == 'd1'