SKSpriteNode has given itself teleporting capabilities and it can't be stopped

Question

If anyone has ever played league of legends, they know that you click an area to make a player move to that spot. They don't get there instantly, it takes a little bit of time. I've tried to add this functionality to a game that I am trying to make. The problem is, the character tends to sometimes move slowly towards the touched area, which is great because that is what I want, but some times there is an inconsistency where it teleports instantaneously to the touched spot. Can anyone see the problem?

let touch                   = touches.anyObject()! as UITouch
let location                = touch.locationInNode(self)
let moveAction              = SKAction.moveTo(location, duration: 3.0)              

if(tankTurn)    // Tank's turn when tankTurn is true.
{
    tank.runAction(moveAction)

    tank.position               = location
    tankTurn                    = false
}// if statement