The "Auto" function works on each individual raw file, not in cookie-cutter fashion.
But if you're going to use the Auto function, you might as well shoot JPEGs instead of raw files.
I'd encourage you to visit the dedicated ACR forum to read about how to learn how to use ACR properly. The ACR engineers are active over there.
I see your post has now been moved to the ACR forum.
I think the Auto function needs some work. I find exposure is generally wrong and Blacks go to +1. I don't understand why Adobe has not addressed these issues.
Blacks go to +1.
Always true for me when auto-toning non-raw files. Raw files have more reasonable auto-toned blacks values.
I see the same reasonable Blacks computation with my Canon raw files. I suspect the Black+1 on JPGs is to counteract an increase of contrast somewhere else.
blacks=+1 with rgb files (not just jpeg) is all ya ever get - not countering anything / totally neglected... - no matter what image you feed it, you get +1 for blacks.........
PS - I reported this gaping omission / bug in the feedback forum...
Yeah, ok, I see this is the case, unless the file is one solid color, which was my first experiment.
Interestingly Shift-double-click-Blacks for an RGB file does compute a less unreasonable Blacks value that stretches things toward the lower end of the histogram.