Multi monitor operation not working as expected, regression to 5.2

[Feuerfloh]

Host: Windows 10, 64 bit Guest: Ubuntu 22.02 64 bit, Linux Mint 64 bit,... - Linux guest additions installed from VirtualBox's image as provided by the host

Situation: in version 5.2.x one could setup a VBox with two monitors, start the VBox and switch it to fullscreen mode - immediately on both monitors. That setting was persisent, so starting the VBox later would bring it up on two monitors in fullscreen mode without any manual action.

After upgrading to VirtualBox 6.1.34, the VBox settings were changed to "VMSVGA" graphics controller.

In version 6.1.34 it is not possible to activate the second monitor if the VBox is already in fullscreen mode - the menu option is not shown at all. And in window mode one has to activate the second virtual monitor by hand each time the guest was started.

If one chooses "VBoxVGA" graphics controller, then the VBox apppears on two monitors in fullscreen mode immediately as it did in version 5.2. But there's then a really ugly bug with wrong mouse coordinates, that makes the VBOx unusable.

I have attached a log file of the following process:

1. starting the VBox (Xubuntu 22.04)
2. logging in
3. trying to activate the second virtual monitor - that FAILED (the window pops up and disappears immediatly)
4. once again trying to activate the second virtual monitor - worked now
5. shutting down the guest

I have tried both, a VBox that was already present and used with version 5.2.44 in the past and a brand new VBox created with version 6.1.34. There's no difference.

So IMHO that's a regression in version 6.1 compared to version 5.2 - it used to work pretty fine in version 5.2.

[Feuerfloh]

log file of the described scenario

[Feuerfloh]

Just upgraded to version 6.1.36; the release notes mentioned some improvements for Linux guests. But this bug still exists.

[nextdayair8]

I'm on 6.1.38 and experiencing this too. Bug is still reproducible with the same steps as Feuerfloh.

I've fixed it by setting my Windows 10 Display Scaling on the host to 100% (from 175%). While that's a working solution, it's a bit inconvenient. Now the text/UI on my Windows 10 host is super small. Essentially, I've traded one issue for another.

OP, are you using any Windows 10 Display Scaling in your host for the problematic monitor?

[Feuerfloh]

Yes, this bug persists in 6.1.38. I've got a display scaling of 100%, so that should have no influence.

There's a work around - nasty, but works:

1. start the vbox
2. make sure, it is *not* running in full screen mode
3. try to activate the second virtual monitor - the first attempt fails in most cases, then just try again to activate the second virtual monitor; this will usually succeed
4. arrange both windows (I always have to drag the second wwindow to the second physical monitor)
5. enter full screen mode

By the way: if the vbox is already in dual monitor full screen mode, then a reboot of the guest keeps everything as wanted - both vritual monitors remain in full screen mode; it is just the start of the vbox itself.