Comment 10 for bug 1714399

[Impact]

In MATE session, logout and shutdown dialogs sometimes
don't get the focus, and it's impossible to switch to
them with Alt-Tab due to their design. One has to use
the mouse to switch there. Using Ctrl-Alt-Tab can help
as well, but I found out it doesn't work reliably in
VirtualBox.

The fix for this issue is provided in the debdiffs
attached to the report.

Would be nice to have the fix backported to all current
Ubuntu releases (Xenial, Zesty and Artful). The bug is
very annoying for users who rely on keyboard shortcuts
to navigate the desktop. It also can be considered a11y
issue.

[Test Case]

There are several ways to reproduce this issue. For me
the most reliable one is to use keyboard shortcut to call
the shutdown dialog:

- press Ctrl-Alt-Del, the shutdown dialog appears, and
  it's usually focused
- press Esc to dismiss the dialog
- press Ctrl-Alt-Del again, now the shutdown dialog will
  appear unfocused

Now you need to use the mouse or Ctrl-Alt-Tab to interact
with the dialog.

[Regression Potential]

The fix just ensures that logout/shutdown dialogs will be
always focused when they appear on the screen. It means
the dialog's behavior is restored to what users expect.
Nothing else is affected, so no chance for regressions.