Digital Light & Color

This is an old thing, a cosmetic one.

The Advanced Sharpen Histogram sometimes does not refresh when the transformation is reopen.
Moving either Sharpen Amount or Sharpen Radius a fraction mostly does the job.

Setting Noise Reduction Blur Amount to a non zero value may also have something to do with it.
Resetting Noise Reduction Blur Amount to zero and switching back to Sharpen Amount tab helps in some cases too.

I played with this for some time and the histogram always refreshed correctly.

When it happens, can you get it back by simply minimizing and then restoring the window or moving it off-screen and then back to force it to be repainted? Any idea why it only fails to refresh sometimes?

I think I have found it.

Place Warp before Advanced Shapen and move the grid so that the left bottom corner of the output image is black.
Or alternately paint the left bottom corner some solid color.
Make the size of the solid color area big enough to propagate the effect to Advanced Sharpen.

It may also happen if a masked area painted solid color reaches completely down left.

It looks like the left bottom corner area is probed when the AS histogram is initiated.

Fixed for next release.