The suspend / sleep feature appears to be gone since the upgrade to Ubuntu 14.04 - there's no such option neither in Power Management (under Suspend Session), nor in the Leave menu. Also the keyboard's sleep button doesn't work anymore, it merely locks the screen. Reproducible: Always
BTW pm-suspend works fine.
This bug is reported on libsolid which is the kdelibs4 version of the solid library. It is now in maintenance mode. If you think it should still be fixed in the KDE Frameworks 5 version of solid please move it to or report a bug on frameworks-solid or Powerdevil.
Hello! Sorry to be the bearer of bad news, but this project has been unmaintained for many years so I am closing this bug. Please try again with the latest version and submit a new bug to frameworks-solid if your issue persists. Thank you!