Nikon D5300 images overexposed on import

When importing RAW images from my Nikon D5300 into Aperture they are all well overexposed.

The images are perfectly exposed in JPEG format and on camera playback.

I have installed all available updates, in particular Digital Camera RAW update 5.02 for the D5300 to no avail.

Same problem occurs in iPhoto.

Is this just a bug and I have to wait for a fix?