Landing sound use the sound correspond to the attaching block's material rather than it's own. For example, jumping onto a grass block with a wooden button attached on top of it will play the sound as if it is a wooden plank. This is also true for the stone button (which I didn't demonstrate in the video), in this case, the sound sounds like you're landing on a stone block.
How to reproduce: All is in the video.
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Thank you for your report!
However, this issue is a Duplicate of MC-2604.
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