Collision problem JBox2D

I work with Processing and the JBox2D library and wanna code a new Ping Pong game. But if I move the player to the top border (or lower border), he collide on a wrong position.

The picture shows player 1 colliding with the top border.

If I move the player again upwards then he moves through the border.

My Player Class:

class Player {
  Body body;
  float pWidth;
  float pHeight;
  Vec2 pos;
  float speed;

  Player(float x, float y, float w, float h) {
    pWidth = w;
    pHeight = h;
    speed = 5;
    pos = new Vec2(0, 0);

    // Add the player to the box2d world
    makeBody(new Vec2(x, y), w, h);
  }

  void playerStep(){
  pos = box2d.getBodyPixelCoord(body);
  }

  void moveUp() {
    body.setTransform(box2d.coordPixelsToWorld(pos.x, pos.y-speed),0);
  }

  void moveDown() {
    body.setTransform(box2d.coordPixelsToWorld(pos.x, pos.y+speed),0);
  }

  void makeBody(Vec2 center, float w_, float h_) { 

    // Define the body and make it from the shape.
    BodyDef bd = new BodyDef();
    bd.type = BodyType.DYNAMIC;
    bd.position.set(box2d.coordPixelsToWorld(center));

    PolygonShape sd = new PolygonShape();
    sd.setAsBox(box2d.scalarPixelsToWorld(w_), box2d.scalarPixelsToWorld(h_));

    // Define a fixture.
    FixtureDef fd = new FixtureDef();
    fd.shape = sd;

    // Parameters that affect physics.
    fd.density = 5;
    fd.friction = 2;
    fd.restitution = 1;

    body = box2d.createBody(bd);
    body.createFixture(fd);
  }
}

Boundary Class:

class Boundary {

  // A boundary is a simple rectangle with x,y,width,and height.
  float x;
  float y;
  float w;
  float h;

  // But we also have to make a body for box2d to know about it.
  Body b;

  Boundary(float x_, float y_, float w_, float h_) {
    x = x_;
    y = y_;
    w = w_;
    h = h_;

    // Define the polygon.
    PolygonShape sd = new PolygonShape();

    // Figure out the box2d coordinates.
    float box2dW = box2d.scalarPixelsToWorld(w/2);
    float box2dH = box2d.scalarPixelsToWorld(h/2);

    // We're just a box.
    sd.setAsBox(box2dW, box2dH);


    // Create the body.
    BodyDef bd = new BodyDef();
    bd.type = BodyType.STATIC;
    bd.position.set(box2d.coordPixelsToWorld(x, y));
    b = box2d.createBody(bd);
    b.createFixture(sd, 1);
  }

  void display() {
    fill(255);
    rectMode(CENTER);
    rect(x, y, w, h);
  }
}