Certain fall damage preventing blocks do not prevent damage when falling more than 28 blocks

This is no doubt because when falling more than about 30 blocks you start to move more than 1 block / tick, and when checking for blocks across the space that you skip the game only checks to calculate impact damage, not to see if you could catch on to any to stop falling.

I just lost my hardcore world due to this.  In previous versions, playing vanilla survival, I could drop one piece of scaffolding any height and drop onto it with no damage whatsoever. I counted on the safety of scaffolding in my hardcore world without realizing that it had become bugged, or changed, at some point.  

I created a test world, flat world, and placed a 3x3 platform of scaffolding.  Next to it, I towered up with scaffolding to varying blocks of height above the platform.  In this test world, you take damage falling onto scaffolding beginning at 20 blocks height, and no damage from 19 blocks or fewer. 

I have attached this test world.