I am preferring xscreensaver for display power management, as with xfce4-power-manager, applications like vlc still blank the screen while watching movies. So i disabled 'manage monitor' in the xfce power management settings, but it still disturbs the system dpms settings. E.g. when dpms is set to enabled within xscreensaver advanced settings and I unplug the power from my laptop so that it runs on battery, xfce4-power-manager disables dpms again. When 'manage monitor' is disabled, it should not touch the dpms settings at all.
What you described seemed to match the symptom described here: "Monitor power management control" unchecked should left unchanged DPMS https://bugzilla.xfce.org/show_bug.cgi?id=6595 Which is why, even when you unchecked "manage monitor", xfpm (xfce4-power-manager) insists to disable DPMS.
Yes, it seems to be similar, but instead of the wording, the behavior of the button should be changed. *** This bug has been marked as a duplicate of bug 6595 ***