I've found something strange when developing BLE MESH using SDK Bluetooth Mesh v220.127.116.11.
I don't know whether I am doing wrong or it's a bug.
It's not a bug, this is how our mesh stack is designed to work. When the client sends a "level delta" request the stack on the receiving side translates it into a "level" request automatically.
Whether the client is setting the level directly or setting a level delta, the application on the server side will always receive same type of event ( = level request).