[Bug]: Minimized secondary monitor windows disappear when guest turns off display output

[chuzmunguz]

Version

7.2.10

Host OS Type

Linux

Host OS name + version

Debian Trixie 13.5 (kernel 6.12.90+deb13.1-amd64)

Host Architecture

x86

Guest OS Type

Windows

Guest Architecture

x86

Guest OS name + version

Windows 11 Build 26200.8655

Component

GUI

What happened?

With a VM configured to use multiple virtual monitors (tested with 3) and VBoxSVGA as the graphics controller, when the guest turns off the display output, any secondary monitor windows that were minimized on the host disappear entirely. The host taskbar loses track of them and they can only be restored via View > Adjust Window Size, which only works sometimes.

The number of active virtual monitors drops to however many were not minimized at the time the display output was disabled (e.g. with 3 monitors, minimizing 2 leaves only the main display visible, as the primary monitor window never disappears). The same behaviour is likely present with 2 virtual monitors, though this has not been extensively tested.
This behaviour is consistent regardless of whether 3D acceleration is enabled or disabled.
Tested on three builds:

virtualbox-7.2_7.2.6-172322~Debian~trixie_amd64 — works correctly
virtualbox-7.2_7.2.8-173730~Debian~trixie_amd64 — works correctly
virtualbox-7.2_7.2.10-174163~Debian~trixie_amd64 — regression present

The issue is not caused by Guest Additions, as it manifests before upgrading them on the guest from version 7.2.8 to 7.2.10. The behaviour is the same with 3D acceleration both enabled and disabled.

Relevant log file: VBox.log

How can we reproduce this?

1. Create a Windows 11 VM with 3 virtual monitors enabled and VBoxSVGA as the graphics controller, running VirtualBox 7.2.10.
2. Boot the guest and let Guest Additions initialize all 3 screens.
3. Minimize one or more of the secondary monitor windows on the host.
4. Set a screen timeout in the guest power settings and wait for the guest to turn off the display output.
5. Observe that the minimized monitor windows disappear from the host taskbar and cannot be restored normally.

Did you upload all of your necessary log files, screenshots, etc.?

• Yes, I've uploaded all pertinent files to this issue.