problem with SCNTransaction in Scene Kit

I'm trying to move an object over a period of ten seconds from y coordinate 0 to y coordinate 10. the object is created at y coordinate 0. The problem is when the animation starts, the object pops to the end position for like one second or so then pops back down to the starting position and begins the animation properly. Why is the object ending moving to the end location instantly, and how can I prevent this from happening?

//create box bottom
func createGrabBox() {
grabbottom = grabBox.rootNode.childNodeWithName("grabbottom", recursively: true)!
grabbottom.position.y = 0
grabbottom.geometry!.firstMaterial!.transparency = 0.5
grabbottom.physicsBody = SCNPhysicsBody(type: SCNPhysicsBodyType.Dynamic, shape: nil)
grabbottom.physicsBody!.restitution = 0.0
grabbottom.physicsBody!.friction = 1.0

//animation snippet
SCNTransaction.begin()
SCNTransaction.setAnimationDuration(10.0)
SCNTransaction.setCompletionBlock() { }
grabbottom.position.y = 10
SCNTransaction.commit()

//physics field for this object
let field = SCNPhysicsField.linearGravityField()
field.strength = 0
field.direction = SCNVector3(x: 0, y: 0, z: 0)