Screen blank mode doesn't get set (sleep and off modes do)

Using xfce4-power-manager 4.18.4 on Arch, i can't set screen "blank" mode; "sleep" and "off" modes get set, instead.

For example: if i set blank after 1 min, sleep after 2 and off after 3, the screen won't go into blank mode after 1 min, but will go into sleep mode after 2 and will turn off after 3.

This is reflected by xset -q, that in the case of the example above says:

DPMS (Display Power Management Signaling):
  Standby: 120    Suspend: 0    Off: 180
  DPMS is Enabled
  Monitor is On

So, in xset's and xfce4-power-manager terms, "blank" is "suspend", "sleep" is "standby" and "off" is "off".

What's strange is that xset's man page, in the "dpms" paragraph, says:

When numerical values are given, they set the inactivity period (in units of seconds) before the three modes are activated. The first value given is for the ‘standby' [sleep] mode, the second is for the ‘suspend' [blank] mode, and the third is for the ‘off' mode.

But if i run xset dpms 120 60 180 it exits with this error:

illegal combination of values - standby [sleep] time of 120 is greater than suspend [blank] time of 60

So it seems that, in xfce-power-manager's terms, xset doesn't accept a sleep time greater than than the blank time, while xfce-power-manager doesn't accept a blank time greater than the sleep time. Maybe it has something to do with the issue?