QPixmap: Must construct a QApplication before a QPaintDevice

Question

I am creating a PyQT and QGIS application and im trying to add a combobox to the UI. I have defined the layout of my UI in a separate module to the main module. I know it is an issue with the combobox as this error only occurs when I add it. The application runs but when I close it this error is displayed in the terminal - QPixmap: Must construct a QApplication before a QPaintDevice

Here is the code for the UI

import sys
import os

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

from ui_mainWindow import Ui_MainWindow

class DeforestationMapWindow(QMainWindow, Ui_MainWindow):
    def __init__(self):
        QMainWindow.__init__(self) 
    self.setupUi(self) 

    self.connect(self.actionZoomIn, SIGNAL("triggered()"), self.zoomIn)
    self.connect(self.actionZoomOut, SIGNAL("triggered()"), self.zoomOut)
    self.connect(self.actionPan, SIGNAL("triggered()"), self.panMode)
    self.connect(self.actionAddArea, SIGNAL("triggered()"), self.addArea)
    self.connect(self.actionRemoveArea, SIGNAL("triggered()"), self.removeArea)
    self.connect(self.actionGetInfo, SIGNAL("triggered()"), self.getInfo)
    self.cb.currentIndexChanged.connect(self.selectionchange)

#handlers for the events
def zoomIn(self):
    pass
def zoomOut(self):
    pass
def panMode(self):
    pass
def addArea(self):
    pass
def removeArea(self):
    pass
def getInfo(self):
    pass
def selectionchange(self,i):
    print "Items in the list are :"

    for count in range(self.cb.count()):
        print self.cb.itemText(count)
    print "Current index",i,"selection changed ",self.cb.currentText()

def main():

    app = QApplication(sys.argv)

    QgsApplication.setPrefixPath(os.environ['QGIS_PREFIX'], True) 

    QgsApplication.initQgis()

    deforestMapWindow = DeforestationMapWindow()
    deforestMapWindow.show()
    deforestMapWindow.raise_()

    app.exec_()
    app.deleteLater()
    deforestMapWindow.close()

    QgsApplication.exitQgis()

if __name__ == "__main__":
    main()

Here is the code for the UI

from PyQt4.QtCore import *
from PyQt4.QtGui import *
import resources
class Ui_MainWindow(object):
    def setupUi(self, window):     
        window.setWindowTitle("Deforestation")

        self.centralWidget = QWidget(window)
        self.centralWidget.setMinimumSize(900, 400)
        window.setCentralWidget(self.centralWidget)

        self.toolbar = QToolBar()

        window.addToolBar(Qt.TopToolBarArea, self.toolbar)

        buttonIcon = QIcon(":/resources/zoomIn.png")
        self.actionQuit = QAction(buttonIcon, "Quit", window)

        buttonIcon = QIcon(":/resources/zoomIn.png")
        self.actionZoomIn = QAction(buttonIcon, "Zoom In", window)

        buttonIcon = QIcon(":/resources/zoomOut.png")
        self.actionZoomOut = QAction(buttonIcon, "Zoom Out", window)

        buttonIcon = QIcon(":/resources/pan.png")
        self.actionPan = QAction(buttonIcon, "Pan", window)
        self.actionPan.setCheckable(True)

        buttonIcon = QIcon(":/resources/getInfo.png")
        self.actionGetInfo = QAction(buttonIcon, "Get Info", window)
        self.actionGetInfo.setCheckable(True)

        buttonIcon = QIcon(":/resources/draw.png")
        self.actionAddArea = QAction(buttonIcon, "Draw Area", window)

        buttonIcon = QIcon(":/resources/remove.png")
        self.actionRemoveArea = QAction(buttonIcon, "Remove Area", window)

        self.cb = QComboBox()
        self.cb.insertItems(1,["One","Two","Three"])

        self.toolbar.addAction(self.actionZoomIn)
        self.toolbar.addAction(self.actionZoomOut)
        self.toolbar.addAction(self.actionPan)
        self.toolbar.addSeparator()
        self.toolbar.addAction(self.actionGetInfo)
        self.toolbar.addAction(self.actionAddArea)
        self.toolbar.addAction(self.actionRemoveArea)
        self.toolbar.addSeparator()
        self.toolbar.addWidget(self.cb)

        window.resize(window.sizeHint())

I am running this on OS X I would love for someone to explain what I am doing wrong and help me fix this.