Everything is ByLayer. Steps to reproduce this in the shortest number of steps...
1. Start a new document
2. Draw a couple of lines
3. Make a block out of those two lines.
4. Add a new layer and change it's colour to green (or whatever).
5. Select that new layer as current layer.
6. Select the block and insert it into the drawing once.
7. Select the object and "mv" (or mouse drag) it anywhere.
That's literally all I need to do, no messing about with any other settings needed.
I've just found another problem. If I add the block more than once, move ONE of them and then hit undo, then they ALL lose their attributes at the same time.