The assets in rhino work as blocks which is very convenient because they are lightweight elements that you can control with rhino scripts.
To properly organize the enscape assets on a layer, use the “block edit command” on that asset, double click on the layer you want to move the asset to and select “change object to layer”.
I also experience the problem that assets are placed in the first layer doesn’t matter which layer is set to current. The above solution doesn’t work for me. Is there an other way to solve this?