fall damage when falling into water

Description:
i made a long hole with water at the botton to fall in, and when I jumped into, at the end i take a tick of fall damage, 1/2 or 1 heart (seems to be random), without moving during the chute.

I was not able to reproduce the bug but the video is exactly what I have done to take fall damage.

The bug has happened 4 to 5 times before I wrote this bug report.

reproduce:

• make a long 1*1 vertical hole
• put water at the bottom of the hole
• dig 2 blocks (at least) just before the water, to make an exit
• jump in the hole and stick to the wall which you just dug your exit
• do not move during the end of the chute, or it will be normal that you take fall damage

video comment :
I reproduced the movements that made me took 1 heart of fall damage just 5 min ago (I do not have feather falling on my boots), and I have not touched my keyboard since the first ~10 blocks of fall (in my video AND when the bug happend)

ps: srry for my english & i hope there is enough explanations