That's expected and not a bug. Once a display is removed from the current configuration (or just turned off), the shell tries to help you by moving all windows to the remaining monitor. So you don't lose them.
This is however a bug if it happens when you try to sleep the whole system. ** Package changed: xserver-xorg-video-amdgpu (Ubuntu) => compiz (Ubuntu) -- You received this bug notification because you are a member of Ubuntu-X, which is subscribed to xserver-xorg-video-amdgpu in Ubuntu. https://bugs.launchpad.net/bugs/1892427 Title: [amdgpu] HDMI connected TV wakeup problems To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/compiz/+bug/1892427/+subscriptions _______________________________________________ Mailing list: https://launchpad.net/~ubuntu-x-swat Post to : ubuntu-x-swat@lists.launchpad.net Unsubscribe : https://launchpad.net/~ubuntu-x-swat More help : https://help.launchpad.net/ListHelp