Set more generous minimums. Flicker seems to have nothing to do with minimum size. I get it even for fairly large dimensions after scaling down from a much larger size. Similar to issues with zoom from about a month ago, before unc0rr fixed them.
#include <QtGui/QApplication>
#include "mainwindow.h"
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}