groov displays the jpg, or single shot image from the camera. It will update that single image at the update rate set in the gadget or groov project.
Pac Display Pro uses a web browser window. If the web browser is looking at the video stream URL, then the image is updated at the rate the network can support.
Try and change the URL that PAC Display is looking at from the camera. Some cameras have different video resolution and different streaming rate URL's. Try and use one of those lower settings.
I think the video is flashing because the network is too slow.