Hm. Not sure what I did.
When I press J while in Develop module in LR CC, the little white boxes around the triangles on the histogram still light up, but I don't see the usual red/blue overlays showing where the photo is over/underexposed. Using OSX.
The histogram clearly shows I'm clipping highlights, so the answer is not that I have no clipping problem and thus no overlay.
Any chance that the clipped parts are actually cropped out of the view?
(I don't recall if LR shows the histogram for the full image or just the cropped part.)
Thanks for the thought, but no. I can push the exposure up 5 stops and the whole image should turn red but nothing.
Oh for pete's sake I just quit and relaunched and it's working again. No idea what happened there but all's well now. Sorry, jb