Looking at your example file, I am not seeing anything unexpected occurring when I view the file in the Camera Raw 8.6 plug-in of Photoshop CC 2014, which should be equivalent to what occurs in LR 5.6.
With other settings the Adobe defaults, if I raise the Blacks slider up to +24 the triangle is still white and the rectangle shows the black clipping indicator is on, and I see one blue dot at the lower left that indicates pure black in one pixel:
Image may be NSFW.
Clik here to view.
However, if I raise the Blacks level by one more, to +25, the triangle turns cyan instead of white, meaning the red channel is no longer clipped anywhere, and as expected that one last blue dot of the clipping area disappears:
Image may be NSFW.
Clik here to view.
Are you seeing something different occurring in LR?
