Very interesting!
It has something to do with the transparent pixels. Not clipped, with White BG layer deactivated.
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In my experiment, I had semi-transparent leaf layer (top) and a solid leaf layer (below) created with the Brush Tool. All in black.
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When I added two non clipped adjustment layers, H&S and Levels.
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Then clipped. The black leaves layer lost their coloration.
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With the White BG layer turned off.
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With the solid leaf layer, the outcome was exact whether or not the adjustment layers were clipped.
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It has something to do with the transparency of the layer.