I am on Ubuntu Mate 19.10.
In previous versions, Marco used to preserve windows' positions when the X11 layout changed, like after plugging in a new monitor.
Now, windows would be shown on the new screen.
For instance, if I set my external monitor to the top of my primary, all windows show up to the external monitor.
What would be expected, and that worked before, is that they are kept on the primary monitor.
There are plenty of reasons for that, like confidentiality or embarrassment when giving a public presentation on stage.
I will submit a bug report, but is anyone aware of that? What happened to Marco that would explain this change?