3d Mesh inverts and scales up after scaling down to a certain amount

I have imported a mesh using www.interactivemesh.org's FX 3D converter, and then created a class to display the mesh, or multiple mesh's in a class extending a group.

I use

cene.setOnKeyPressed((event)
 ->{
     if(KeyCode.UP.equals(event.getCode()))
     {
         f.setScaleX(f.getScaleX()+ .1);
         f.setScaleY(f.getScaleY()+ .1);
         f.setScaleZ(f.getScaleZ()+ .1);
         System.out.println("kaw");
     }
     
     
     if(KeyCode.DOWN.equals(event.getCode()))
     {
         f.setScaleX(f.getScaleX()- .1);
         f.setScaleY(f.getScaleY()- .1);
         f.setScaleZ(f.getScaleZ()- .1);
         System.out.println("kaw");
     }
 });

to scale the group larger and smaller based on the key pressed.

When it gets to a certain point it will disappear, and then invert it's colors and start to grow.


I have some pictures I want to attach, but I cannot find the attachment tab.