If gnome-screensaver is started with trailing &, xflock4 can't lock screen by "gnome-screensaver-command --lock" immediately after that.
Current gnome-screensaver daemon does not fork, so it has to be started with trailing &: "gnome-screensaver" (3.6.1) seems to work as "gnome-screensaver --no-daemon"; same thing with light-locker (1.0.0). However, gnome-screensaver is not started automatically with current Xfce, so I think this bug report is obsolete.
Close bug reports of archived products.