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 <QLabel>
#include <QRect>
#include <QList>
#include <QMouseEvent>
class PixLabel : public QLabel
{
Q_OBJECT
public:
PixLabel();
QList<QRect> rects;
public slots:
void AddRect();
private:
void paintEvent(QPaintEvent * event);
void mousePressEvent(QMouseEvent * e);
};