Histogram combing in 14-bit TIFF conversion from NEF

I'm using View NX 2.3.2 (the latest updates applied) and selected 16-bit TIFF output for a raw image from a D800 camera, where the NEF was recorded in 14-bit high quality. When I open this image in Adobe Photoshop and apply a curve adjustment layer to brighten the image, the histogram shows significant combing, indicating that the color data are not 14-bit, but a much lower color depth such as 8-bit. Am I missing a conversion option in View NX to preserve the color depth from the original capture? I do this operation all the time with other cameras and scans and have never seen combing on 16-bit images.

If you want to try this yourself, the curve has only one control point: Input 21, output 46.