VirtualBox icon mess?

[Golddouble]

MX Linux 19 (Debian)
Xfce

I have a starter for VirtualBox.
In VirtualBox I have two different Windows 7 VM's.
When I open VirtualBox and start VM-1, then I get in addition this icon:

When I start Windows 7 VM-2, then I get in addition this icon:

Question 1: Why do I get an additional icon when I start a VM? Why is the VM not behind the VirtualBox icon. To be more precise: Why is the VirtualBox and the VM not grouped in the same icon?
Question 2: Why do I not get the same icon for VM-1 and VM-2 although it is the same typ of VM?
Question 3: Why do I not get this icon for the opened VM:

(When I use Xfce standard panel, I get this icon for opened Win7 VM's)

Would appreciate some answers.
Thank you.

[xuzhen]

Why is the VirtualBox and the VM not grouped in the same icon?

They have different WM_CLASS value. One is "VirtualBox Manager" and another one is "VirtualBox Machine"

Why do I not get the same icon for VM-1 and VM-2 although it is the same typ of VM?

The generic window icon for VM-1 is a bug and should been fixed in xuzhen@c5fd810

Why do I not get this icon for the opened VM:

DockbarX shows the "group icon" in dock, not the window icon. Read the comments for details

[Golddouble]

Thank you.