SDR white does not map to "paper white" when the HDR button is pushed.

If I take an SDR image of the CIE 1931 Colorspace image 

In SDR the histogram looks like this. with a peak at SDR white.

When I push the HDR button.  The original luma range is incorrectly expanded to extend above the luminance of HDR "paper white" which is at the vertical grey line in the middle of the HDR histogram. 

This is an incorrect mapping of luminance from the SDR original to the new HDR image being displayed.

It also seems that this incorrect expansion of luminance varies with the image content.

Is there an option that would correctly map the SDR image luminance values to the 0-50% range in the displayed HDR image when I switch from SDR to HDR mode?  That would be the preferable starting point for any HDR modification.

It would also avoid giving me the false impression that a regular jpg image is a gain-mapped jpg HDR image when it is not (which has been driving me crazy all day).