I know this is old.
But the "Y" makes me think this is actually a misunderstanding of vectors for developers familiar with other systems.
Please note that LEAP MOTION uses a RIght Handed Cartesian Coordinate system... AND it has the ability to switch view from 'sensor sitting on a surface' (a below view) to a 'visor oriented view'. Other systems tend to use the Left Handed Cartesian Coordinate system. For example, Unity3D is Left-Handed...
So if you are having a vector problem and the Y is your problem.. think about your sensor orientation and its vector assumptions. You might need to adjust some Positive or Negative values to get things working the way you would like.