The console prints the lines below during the creation of the plugin:
QPainter::begin: Paint device returned engine == 0, type: 2
QPainter::begin: Paint device returned engine == 0, type: 2
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setFont: Painter not active
QPainter::setPen: Painter not active
QPainter::drawPoints: Painter not active
Although it does not (seem) to affect the plugin, it is a good idea to try to fix this because it does not look very nice.