I have a (seemingly rather exotic) Dell Latitude XT2 notebook running Lubuntu 12.04, fresh install.
Tried to get the power button to work as expected (opening the logout dialog
lubuntu-logout), but no success: power button does nothing but forced power-off on long press.
The power button itself is detected and works. In xfce4-power-manager-settings, when I set the power button action from "Ask" (= open
lubuntu-logout) to "Shutdown", the laptop shuts down successfully; pressing the power button is recognized and processed correctly.
Edit: I removed a bunch of info from the question, as it seems not to be related to the problem.