HDMI external monitor displays only desktop wallpaper

**Description**
In the situations described below, the television video source is set to HDMI3, the set is switched on, and the cable is plugged into HDMI port 3.

If the laptop is switched ON and booted into either Windows or Ubuntu, it will not recognise when the cable is plugged into the HDMI port.

If the laptop is switched OFF, the cable is plugged into the HDMI port, and the laptop is booted into Windows, the laptop display is echoed on the television screen and YouTube and streaming video is sent to the TV.

If the cable is plugged in, and the laptop is booted into Ubuntu, the HDMI cable is recognised but the display on the TV screen is different from that on the laptop. On the Ubuntu home desktop laptop display the wallpaper displays with icons down the left, a browser open, and scattered files and icons. The image echoed to the TV screen shows ONLY the desktop _wallpaper_! No apps, icons, cursor arrow or anything else on the desktop displays on the TV!

I don't know whether this is a HDMI fault, a display package fault, or what package.

**Questions**
1 Does anybody know how to fix the problem?
2 What other CLI commands do I need to execute to obtain more diagnostic data?
3 Are we looking at a Wayland bug here? If so, where and how do I report it?

_Note_
The Windows System Information app is far superior in depth and breadth of information and keeps all the information you would want in one convenient and easy to use place.

**Hardware**
Hisense DVB-T Model:HL32T28PZL PAL B/G television receiver (3 x HDMI ports)
Dell Vostro 2520 laptop (1 x HDMI port)
Intel(R) HD Graphics 4000 (from Window System Information)
Intel Corporation 3rd Gen Core processor Graphics Controller (rev 09)
Subsystem: Dell 3rd Gen Core processor Graphics Controller, Kernel driver: i915 (from lspci)
(Note: no proprietary graphics drivers found in Software & Updates > Settings > Additional Drivers.)
Dual booting:
* Windows 10 Pro
* Ubuntu 18.04 Bionic Beaver LTS

**Command outputs**
~$ lspci -k | grep -A 2 -i "VGA"
00:02.0 VGA compatible controller: Intel Corporation 3rd Gen Core processor Graphics Controller (rev 09)
 Subsystem: Dell 3rd Gen Core processor Graphics Controller
 Kernel driver in use: i915

~$ aplay -l
**** List of PLAYBACK Hardware Devices ****
  [...]
card 0: PCH [HDA Intel PCH], device 3: HDMI 0 [HDMI 0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

~$ aplay -L
  [...]
hdmi:CARD=PCH,DEV=0
    HDA Intel PCH, HDMI 0
    HDMI Audio Output
  [...]