placing a ladders on a block and let it hang from it, then breaking the block makes all ladders below it to freely float instead of breaking

4.0-458
1.20.1 tag

This is a feature, not a bug.

No, it's not, quark allows you to place down ladders and have part of them floating but they always need the first one to be supported.
As you can see in the image, the bug here is that they can freely float without any kind of support

Oh I see. In vanilla the only way to make a ladder fall off is to break the block behind it, so in vanilla LadderBlock#updateShape only does the canSurvive checks if the update came from behind.

But using quark's freestanding ladders, it's possible to detach a ladder by breaking the block above it.