Ding, ding, ding... we have a winner!
It is indeed the sharpening. Apparently, the preview of the sharpening applied in the Develop module is not anything like what is actually applied when you start really pushing it. Specifically, it's the Detail slider that will give you a nasty little surprise - I had it set to 75, and as I reduced it, the problem got less severe (10 to 15 is where it will stop having this bizarre effect). What I was initially after was the "crunchy" look, but what I got was something else...
Lesson learned: apply "special effects" sharpening in Photoshop, where you can see exactly what you are getting.
Okay, now I'm lost. This thread seemed to address a problem I was seeing, but the solution did not work for me. I'm seeing what appears to be different output tone curves near black (maybe related to color management) applied to the same image whether it is viewed in the develop module or in the library module.
Here's the image, adjusted how I would like it - displayed in the develop module at 1:1 viewing the lower right hand corner of a beach sunset:
And here is the image displayed in the library module (this is also what I get when exporting a tiff or jpeg):
I hope the differences are visible after converting the screenshots to jpg and viewed with your web browser - you may need to download them.
Any advice on what I'm missing would be appreciated.
This comes from Version 3.0 Beta 2 - 662985,
running on a macbook pro with OS X 10.5.8.
My display was calibrated with a colormunki which, I understand tends to block up the darks. So that may be accentuating the differences for me - but there certainly is a difference.