MPL set_cursor problem under 1.2.0

dock.py

from PyQt4.QtGui import QApplication, QMainWindow, QDockWidget
from PyQt4.QtCore import Qt

from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg
from matplotlib.backends.backend_qt4 import NavigationToolbar2QT
from matplotlib.figure import Figure

a = QApplication([''])
w = QMainWindow()

f = Figure()
ax = f.add_subplot(111)
ax.plot([1,2,3], [2, 3, 4])
canvas = FigureCanvasQTAgg(f)
tb = NavigationToolbar2QT(canvas, w)

dw = QDockWidget("test")
dw.setWidget(canvas)

w.addDockWidget(Qt.TopDockWidgetArea, dw)
w.addToolBar(tb)

w.show()
w.raise_()
a.exec_()