egl/wayland/mutter: unable to show different resolutions

A system running

• Debian Buster
• Wayland 1.16.0
• mutter/experimental 3.32.2+git20190711-2
• GStreamer git
• nvidia 430.34-1

The following pipeline starts and shows the videotestsrc (default resolution)

gst-launch-1.0 videotestsrc ! "video/x-raw, width=320, height=240" ! glimagesink sync=0

The following does not (or any other resolution that was tried).

gst-launch-1.0 videotestsrc ! "video/x-raw, width=640, height=480" ! glimagesink sync=0