If the 'Lock screen when system is going for sleep' option is turned on in the power manager settings, xfce4-power-manager doesn't suspend the computer when the 'When laptop lid is closed' is set to 'Suspend', and I close the laptop lid. The 'Suspend' button in xfce4-session-logout works correctly: it locks the screen, then suspends the computer. If the 'Lock screen when system is going for sleep' is turned off, the power manager works well: if the lid is closed, it suspends the computer.
Duplicate of bugs #15300, #15151, #12756, #12088
I have proposed a patch here: https://bugzilla.xfce.org/show_bug.cgi?id=15300#c9
*** This bug has been marked as a duplicate of bug 15300 ***