RE. Thanks Mike. I had noticed the odd problem with this and was using the Refine camera black red rectangle for highlight recovery more often when the subject had very dark areas. I've checked a few of those images and in cases where a red rectangle was used reverting to the Magenta rectangle has worked very well.
Also, I noted the shift key in refine shows areas of very low (black) RGB  values as well as the very bright areas in an image. That's very useful I think.
I'd be interested to know what the RGB values are that trigger these indications?
Terry