Comment 9 for bug 1700419

The patch for this bug: https://gitlab.freedesktop.org/xdg/xdg-utils/-/issues/98 does fix the problem, though I am not sure that the problem here is that the window has no title, rather that no title is reported by X11::Protocol. However, for our purposes that's good enough!

I shall ensure that this is raised on the xdg-utils Debian package. In the mean time, a workaround for users is to apply the patch from the above issue to xdg-screensaver, and place the patched version on their PATH (e.g. in ~/bin).