Available resolutions detected in "Display" utility are not consistent with xrandr output

[Po-Hsu Lin]

CID: 201212-12386 HP Pavilion 23 All-in-One

This AIO comes with two AMD graphic controller:

When running on open-source driver, the available resolutions from xrandr -q are:
  1920x1080 59.8*+
   1680x1050 60.0
   1400x1050 60.0
   1280x1024 59.9
   1440x900 59.9
   1280x960 59.9
   1280x854 59.9
   1280x800 59.8
   1280x720 59.9
   1152x768 59.8
   1024x768 59.9
   800x600 59.9
   848x480 59.7
   720x480 59.7
   640x480 59.4

However, the last three resolution sets:
   848x480 59.7
   720x480 59.7
   640x480 59.4

Are not available in the "Display" utility in the unity-control-center.
I'm not sure if this is a by-design issue.