mouseMoveEvent ignored in QGraphicsView if frame shape is set to NoFrame

If I create a QGraphicsView subclass with custom mouseMoveEvent code, events are no longer received if I set view.setFrameShape(QFrame.NoFrame). I have this bug in PyQt, but I presume the actual problem is with Qt.

Example PyQt4 session:

>>> from PyQt4 import QtGui
>>> app = QtGui.QApplication([])
>>> def callback(*args):
... print "move"
...
>>> gv = QtGui.QGraphicsView()
>>> gv.mouseMoveEvent = callback
>>> gv.show() ## now drag mouse over the view and messages are generated
move
move
...
move
>>> gv.setFrameShape(QtGui.QFrame.NoFrame)

1. 1. now drag mouse over the view, messages are no longer generated