Aarolin

I found a setup that replicates this without another minecart:

The same thing happens (Place the minecart on the top powered rail):

And it isn't stuck on the top block:

(Breaking the bottom rail stops the floating):

The same setup with the minecart toggle off works as expected:

Maybe it happens when the minecart stops while turning and falling onto another rail? If it's an activator rail or another straight, non-unpowered powered rail, it'll continue moving and fix itself.

Can confirm this happens with the given setup.

Can confirm. This only affects the experimental minecart toggle. In previous versions, placing the minecart would make the cart slope with the rail, but with the toggle it doesn't. The bug also occurs if the minecart is placed with a dispenser onto an unpowered rail (though doing this requires a 1-tick pulse).

Expected Behaviour (Toggle Off):

Actual Behaviour (Toggle On):

Can confirm. This only happens with the experimental toggle on, and isn't present in either 1.21 or the untoggled game. It happens regardless of the minecart max speed, whether it's the default, 1, or 1000. 

Can confirm. This only happens with the experimental toggle on, and isn't present in either 1.21 or the untoggled game. It happens regardless of the minecart max speed, whether it's the default, 1, or 1000.

Can confirm this is fixed in 1.21 pre4.

If this change is intended, that means you have to hit your target the tick before you hit the ground to guarantee safety. Consequently, past a certain height, it might be impossible to guarantee a safe mace hit with a Wind Burst Mace.

Assume that you're targeting a pig, with a hitbox size 0.9 blocks tall. With a survival player reach of 3 blocks and camera height of 1.62 blocks, the lowest a player can attack the pig is 2.28 blocks above the ground (if they look straight down). Consequently, if the player is moving faster than 2.28 blocks/tick downward, it is possible to enter this attack region and hit the ground during the same tick, making you take damage no matter what you do. With a standard gravity of 0.08b/t^2, this can happen after just 29 ticks of falling, or about 33 blocks. 

Taller mobs take longer to have guaranteed misses. Assuming all of that is right, it seems strange that a skill-based weapon can be invalidated by essentially bad luck. You can hit the mob, have Wind Burst activate, and still die for it.