tst_macgui autotest is unstable Qt 4.8

********* Start testing of tst_MacGui *********
Config: Using QTest library 4.8.2, Qt 4.8.2
PASS   : tst_MacGui::initTestCase()
FAIL!  : tst_MacGui::scrollbarPainting() 'isContent(pixmap.toImage(), horizontalScrollbar.geometry(), GuiTester::Vertical)' returned FALSE. ()
   Loc: [tst_macgui.cpp(105)]
PASS   : tst_MacGui::dummy()
PASS   : tst_MacGui::splashScreenModality()
PASS   : tst_MacGui::nonModalOrder()
PASS   : tst_MacGui::spinBoxArrowButtons()
PASS   : tst_MacGui::cleanupTestCase()
Totals: 6 passed, 1 failed, 0 skipped
********* Finished testing of tst_MacGui *********