cad using ctrl + c and ctrl + v perform when copying files across the viewport, there will copy the viewport freeze information is lost, because you just choose the viewport to copy,
If the freeze information to achieve take, the primitive should contain layers associated with ctrl + c / v, so that you can copy and paste information viewport.
The principle is roughly the viewport copy to go, need the layer table. Take handle to reference, you just copy the viewport, resulting in the loss of reference.
