QVideoWidget does not keep aspect ratio

Hello,

I'm experiencing what appears to be a bug in QVideoWidget. When I resize the window containing the video the image becomes stretched. During the resize, while the mouse is pressed, the video frame flickers between the stretched state and a state where its aspect ratio is maintained, and stays stretched when I release the mouse (see attached image).

A basic version of the widget I'm using to replicate the issue is shown below (using PySide2):

class Editor(QWidget):

    def __init__(self, video_filename, parent=None):
        super().__init__(parent)
        main_layout = QVBoxLayout()

        video = QVideoWidget()
        video.setAspectRatioMode(Qt.KeepAspectRatio)
        main_layout.addWidget(video)

        self.player = QMediaPlayer()
        self.player.setMedia(QUrl.fromLocalFile(video_filename))
        self.player.setVideoOutput(video)

        self.setLayout(main_layout)
        self.player.play()

The system I'm running this on is Ubuntu18.04 with the X11 window system and GStreamer1.15.5