That's an option to setup only left/right inside the behavior, so, I supposed it was designed to be for horizontal movements '-.-
Taking a look in the description, you can easily do the same mistake as myself...
<img src="https://dl.dropboxusercontent.com/u/47035927/temp/screenshot_8dir.png" border="0" />
When all what I wanted was move object left and right in the canvas, while doing a study for space invaders.
Do you have any concern about using the platform behavior to simulate the AI of 30 objects on the screen? Didn't tested it yet, but was trying to use the minimum possible to make viable the AI without spending any % of process than the necessary, targeting mobiles.