BUG: fits flat calibration broken in 1.2.0-rc1

Siril version: 1.2.0-rc1 (latest stable version)

Operating System: Windows

Package: official windows 64bit download (Siril - Siril 1.2.0-rc1)

Description of the bug

Flat calibration seems broken, while in 1.0.6 works ok.

Here an example with version 1.0.6

stack_1.0.6.fit

Here an example with version 1.2.0-rc1

stack-1.2.0-rc1.fit

The two files are generated with the same script and sources. The only difference is the siril version.

For completeness, here the script:

requires 1.0.0
set32bits

setcpu 6

cd B
convert B -out=../process
cd ../process
preprocess B '-dark=../2023_06 - dark 2x2 -20 300s' '-flat=../2023_06 - flat 2x2 LRGB' -cc=dark
register pp_B
stack r_pp_B rej 3 3 -norm=addscale -filter-wfwhm=85% -filter-round=85% -output_norm -out=results/B
cd ..

close

Changing preprocess with calibrate lead to the same result (as reported here the command preprocess is deprecated but is an alias to calibrate)

Reproduction

Reproduction steps: get the files (you can grub them from here), execute the script above in the root of the linked folder.

Expected result: an image calibrated like this stack_1.0.6.fit

Actual result: an image not calibrated like this stack-1.2.0-rc1.fit

Additional information

Please provide any backtrace or warnings/error you could have, paste it here.