unlocking background

[Piscium]

Hiya,

I have two PCs with similar configurations:
Arch Linux
lightdm with background image set
XFCE session
openbox as window manager
xfdesktop not installed
feh to set the background
xfce screensaver

Here is the puzzling thing: in one of the PCs when I unlock the
background is the image I have configured (Arch wallpapers) and in the
other PC the background is greyish blue, that is, the wallpaper I
configured is not shown.

Any ideas about what could cause this difference?