XPS 15z with uneven backlighting on keyboard

My XPS 15z seems to have an uneven backlight on its keyboard. The uneven lighting is very noticable in darker conditions. In particular, the 4, R, D, C keys are all noticeably dim, compared to the rest of the keys, see this image:

The above image was with brightness on maximum, when it is on medium, the mentioned keys look even dimmer than the rest.

Is this normal or can something be done? A few places I read said its normal, though I think the difference in lighting is a bit much!

Thanks,

James