I was playing on a world of mine and I placed a vine on the wall while falling (I climbed the vine ) and when I fell off of it, I took fall damage but I was mid-air.

In this world, I had some repeating command blocks with the commands:
/replaceitem entity SuperGalaxy9939 slot.hotbar 1 planks 64
/replaceitem entity SuperGalaxy9939 slot.hotbar 0 vine 64
And a command block running at every ~76 redstone ticks with the command:
/fill 11 4 -1 209 49 1 air []

Reults:
I took fall damage and died.

Expected results:
I should had taken no fall damage until I would hit the ground.

Reproduce:
Do what I described above.

See the video for details.