Insert a block on layer "BLOCK" then turn layer "BLOCK" off or freeze it and the block disappears whether all entities in the block were created on layer "0" or not

i.e.: create a block using layers "B1" and "B2. Insert it in layer "BLOCK". If you turn off layer "B1" or "B2" then that part of the block disappears. If you turn off layer "BLOCK", nothing disappears.