Virtualisation fail ? Why invisible content is added to my list ?

[Bartaf83]

The rowRenderer in my List returns a tbody.
My list is made of tbodies with many TRs inside each of them.
The height of each TR depends on its content which means the TRs and tbodies have variable heights.

Here is a Demo I made in stackblitz

Here are the heights of the tbodies of the table in that demo by index :
0 => 26538px
1=>26610px
2=>26862px
3 => 26538px
4 => 25224px

The viewport is only 426px height.

Why in the initial display I'm getting all of the 4 tbodies added to the dom if just the first one is already heigher than the viewport ?