pyqgis - Segmentation Fault upon exit of QGIS map canvas

I have simplified my original code. My code is very similar to Pyqgis' cookbook. I am simply loading one VALID layer to QgsMapCanvas and then displaying it. Everything is displayed corectly etc. Problem is, everytime I exit out of the QgsMapCanvas GUI, my code then shows a segmentation fault (core dumped) message. How can I prevent this from happening?

from qgis.core import *
from qgis.gui import *
from PyQt4.QtCore import *


def main():

    # initiate canvas for debugging purposes
    # supply path to qgis install location
    QgsApplication.setPrefixPath('/usr', True)
    # create a reference to the QgsApplication, setting the
    # second argument to False disables the GUI
    app = QgsApplication([], True)
    # load providers
    app.initQgis()

    # create Qt mapCanvas object

    canvas = QgsMapCanvas()
    canvas.setCanvasColor(Qt.transparent)
    # enable this for smooth rendering
    canvas.enableAntiAliasing(True)

    # create vector layer object
    layer = QgsVectorLayer('BUAARE.shp', 'layer', 'ogr')

    if layer.isValid():
        QgsMapLayerRegistry.instance().addMapLayer(layer)

        canvas.setExtent(layer.extent())
        canvas.setLayerSet([QgsMapCanvasLayer(layer)])

    canvas.show()
    app.exec_()

    # exit qgis
    app.exitQgis()
main()