W64 host, Ubuntu guest: mouse cursor corrupt in Terminal on secondary 4K screen

[JonAtFS]

System details at the end.

Whether the VB container window is sized very small or large, there is a glitch with the mouse cursor inside Terminal windows in the guest OS.

Note that there are two 4K monitors attached. This bug only appears if the VB container window is on one of the secondary monitors. If it is on the laptop's main screen, the cursor simply disappears when typing, which I believe is the desired behaviour.

The specific issue is as follows: once the mouse cursor is moved inside the Terminal window, it is at first correct. However, type as much as one character, and it turns into a block of glitched data, 8-10 characters wide and one character tall. If the cursor is moved even a tiny amount, it returns to normal, until the user types once again.

I've attached images of the before and after effects within a small VB container window.

It appears that when the cursor is being removed, the underlying pixels are being bitblt'ed from the wrong part of video memory.

System details

VB 6.1.26 build 145957 (Qt5.6.2)

Host:

• Edition Windows 10 Pro
• Version 20H2
• Installed on ‎06/‎07/‎2021
• OS build 19042.1165
• Experience Windows Feature Experience Pack 120.2212.3530.0

Guest:

• Ubuntu 64 bit Hirsute, all patches current
• VM Additions installed.

PC:

• Processor Intel(R) Core(TM) i5-7200U CPU @ 2.50GHz 2.71 GHz
• Installed RAM 8.00 GB (7.88 GB usable)

System type 64-bit operating system, x64-based processor

Config:

• HP EliteBook 840 G4
• 3 GiB RAM assigned to guest
• Main screen: 1080p inbuilt
• Secondary screens:
  • 2x 28" 4K
  • full resolution
  • 125% scaling
  • both connected using DisplayPort.

[JonAtFS]

Cursor normal, before the user types anything

[JonAtFS]

Cursor corrupted after typing

[JonAtFS]

(Apologies for poor quality images, by the way. Whichever way I tried to screencap the results appeared to prevent them being captured, so I had to take phone pictures instead.)