When the head of a piston is a loaded block, a strange lighting bug appears, a shadow is generated at the beginning of the extension of the piston, see image.
I tested this bug in the next java versions:
1.16.3, 1.16.2, 1.16.1, 1.15.2 (without optifine and with the default config, in my tests, the brightness was in bright mode)
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Duplicate of MC-93869

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