I only had a quick look through your code and i saw this in line 215:
else if (cubeDropped = true)
Theres only one "="...
About your problem: I think you use JmePysics2 - the PhysicsGameState?
But your code uses the jme-build-in collision detection.
There is somewhere a collision-callback interface in JMEPhysics2, where you get Collisionresponses from JmePhyiscs2. Irrisor perhaps knows more...
Also the initialisation in the constructor is perhaps a problem - you call node.generatePhysicsGeometry() before PhysicsSpace.create()....
Regards
snare