This issue affects any non-full block, including trapdoors, farmland, slabs, stairs, chains, etc. Relogging or breaking the block is the only resolution until a proper fix is put out. Affects version v1.21.0.
This is still an issue as of 1.20.30, see attachment below:
[media]OP here, this issue has been resolved for some time now. Not sure what update specifically, but it's been fixed.
Can confirm, does not work on realms as of 1.18.2.
The best workaround for this bug (unfortunately) is to play in windowed mode for now.
This will happen when it retracts, too. Use a horizontal sticky piston and attach a block to it while extended. Add the falling blocks onto the block attached and retract the sticky piston. The falling block closest to the sticky piston will break.
Although I haven't tested recently, I remember specifically testing with a friend to recreate this bug. We managed to find that we could consistently recreate this by:
Player A jumps from ~10 blocks and Player B punches Player A before he hits the ground. The result is saturation health. I'm not sure, however, if this applies to GoldenHelmet's damage immunity time explanation, mainly because I recieved the saturation hearts before I hit the ground. I'll test tomorrow though, and I'll post my results.
Try to change your skin. There is a post claiming they have the same problem, but when changing your skin it lets you join.
I can confirm this also happens with sheep. Spent two stacks of wheat on one baby, never grew up. This is happening on 1.14.2
Likely the first report of MCPE-153515