The player takes fall damage when tilling and then immediately walking over tilled land. It seems to only happen when there is not a block underneath the newly tilled land. Damage occurs when running and walking, but I have not been able to recreate the bug while sneaking. Video: https://photos.app.goo.gl/9u37jEzkB7kAw9498
Edit: It seems it's actually easier to replicate the bug while sneaking. Tilling the land you are on top of and moving forward while sneaking will cause you to take fall damage almost every time you till the land. Video: https://photos.app.goo.gl/4TYe6Pe4bi5ygn44A
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We're tracking this issue in MCPE-120140, so this ticket is being resolved and linked as a duplicate.
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I know it's fall damage because I took reduced damage when equipping feather falling IV boots.