Sony Lossles Comp (L) bigger resolution than excepted

[megapro17]

I have a Sony a7c2 camera fw 1.02. And I've got something strange after taking raw photos. In L lossless mode, I'm getting 36.7 megapixels, instead of 33.0. Exiftool reports it under [Composite] Megapixels and ImageSize tag.
When opened in Windows 11 Photos app I can see a black border in the right down corner. When opening in fastrawviewer or photoshop, it displays image correctly, with correct resolution.
I've found the same error reported two years ago: https://www.sonyalphaforum.de/topic/4892-arw-datei-40-mit-schwarzem-rand-rechts-unten-in-luminar-ai-und-affinity-photo/, they're saying about apc-s mode, but that's not the case, author used a M mode that downscales a raw image. Photos doesn't display M and S images at all, and don't write resolution in properties, but exiftool reports it correctly
Can someone tell me what's going on? Why some apps are showing wrong resolution, when others are not?

Uncompressed: 7040x4688
Sony Lossles Comp (L): 7168x5120
Sony Lossles Comp (M): 5120x3584
Sony Lossles Comp (S): 3584x2560
Compressed: 7040x4688

[Phil Harvey]

The size of a raw image isn't carved in stone.  I know that Canon raw files may have a masked area around the outside of the image that is only used to calculate the black level.  I don't know if this is the issue here, but it is up to development software to decide for itself how close it wants to go to the masked area.

- Phil