Two ways of doing auto levels

Hi,
I just noticed there are two methods of applying automatic levels in darktable, and they give different results. I am curious about why. The manual does not mention the difference.

First method:
Start with Levels module reset and turned off.
Press Auto button below histogram.

Second method:
Start with Levels module reset and turned off.
Select mode: automatic

In this image, the left half of the image is done with the first method, and the right half is done with the second. No other differences.

No one knows? @houz?