Runtime error on second connection with Qt.UniqueConnection

Following code snippet raises RuntimeError but it shouldn't:

>>> from PySide.QtCore import *
>>> class Obj(QObject):
... signal = Signal()
...
>>> obj = Obj()
>>> def hi(): print 'hi'
...
>>> obj.signal.connect(hi, Qt.UniqueConnection)
True
>>> obj.signal.connect(hi, Qt.UniqueConnection)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
RuntimeError: Failed to connect signal signal().

Instead of RuntimeError it should have just returned False.