Landscape painting problem, anyone ever seen this before?

Hello everyone, i’m a 3D artist currently trying to learn Unreal engine, and it’s actually making me lose my mind on so many aspects, but the most egregious one is by far this problem i’ve encountered.
I created a standard landscape material with 4 very basic layers, and everything seems to be fine until i try to erase the layers…

![Cattura|690x378](upload://3BoiAoSpC9qc0W5TtSX


XuUISR6e.jpeg)

What is the point of having layers if painting one destroys the ones below? it HAS to be a bug right? Does anyone know what is going on here and how to fix it?