y4m pc luma not properly handled

using version 2.8+23-656b5b442f0b I use a y4m file as input https://drive.google.com/drive/folders/148Op7rDDMeY99G2ofUfTk68d3fZmLc13?usp=sharing has the following header: YUV4MPEG2 C420p10 W1280 H720 F25:1 Ip A0:0 XLENGTH=100 it was created using Vapoursynth and a single image.

Encoding the file with:

"G:\Hybrid\64bit\x265.exe" --input "h:\pc_scale.y4m" --output-depth 10 --y4m --profile main10 --level-idc 4.1 --crf 18.00 --vbv-maxrate 50000 --vbv-bufsize 50000 --range full --colormatrix bt709 --output "C:\Users\Selur\Desktop\Test\compare\x265.265"
MP4Box -par 1=1:1 -add "C:\Users\Selur\Desktop\Test\compare\x265.265"#video:fps=25 -brand hvc1 -tmp "C:\Users\Selur\Desktop\Test\compare" -new "C:\Users\Selur\Desktop\Test\compare\x265.mp4"

the contrast of the output is wrong. (same happens when using 8bit as source and target)

I uploaded the initial image, the y4m (263mb) file and the encoded file (256kByte) to my google drive: https://drive.google.com/drive/folders/148Op7rDDMeY99G2ofUfTk68d3fZmLc13?usp=sharing

Seems like x265 can't properly detect/handle pc scale luma input or I am simply not aware how to tell x265 that the input uses pc luma scale.

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