1 hearth.. But it looks for me it's more..

So I need 1 heart for a new map im making.. So I tested my thing out what I was trying to do..

What I expected to happen was...:

I die when I hit over 5 blocks, to kill 1 heart

What actually happened was...:

The first time, I die perfectly, the second and all the other deaths.. it looks like my hearts are back to 20 but it only show 1... And it gives me a weird photo

Steps to Reproduce:
1. /attribute @p minecraft:generic.max_health base set 1
2. Go jump of to die
3. go again kill yourself, to kill 1 heart.. But this time it takes longer and it does weird stuff if you die on magma blocks...