The last layer of any LCD panel is a polarizer filter (actually, each pixel on LCD don't appear and disappear on the panel, but change his polarization, so it's a basic characteristic).
The same filter of sunglasses and photographic lens.
So it's normal by the origin of LCD.
Not all LCD are affected by this why (as photographic filters) is possible to use also "circular" filter (more expensive than classics), that limit that effect.
So, short answer: it's normal on non-hight range LCD
