That is a normal thing to see some refraction of light coming from the defroster lines. It's even more noticeable on newer model vehicles since car manufacturers are now adding thicker defroster lines.

​

What is happening is the tint has to flex up and over the lines and there is a slight air pocket between the defroster lines and tint. When headlights shine on the tint, it refracts the light on top and bottom causing it to have multiple headlight effect.