My fault, I was too concise.
1.Drag and drop an external 3dm file into current Rhino session, set options like the picture below:
2.Make the block layer a nested layer by dragging it into a parent layer:
3.Save, close and re-open file.
I expected Rhino would retain the nesting property of the block layer, instead it will move it up to the highest parent level, like this:
Actually, the documentation about the ‘Insert’ command states that “Only the on/off, locked/unlocked states and the layer color can be modified.”, so my doubt that it could be a bug has been clarified. I should have read the documentation before posting
Anyway, I think it would be useful to be able to nest those block layers, specially when including many different linked blocks in one file, just to keep it tidy in the layer panel.