Commander Gizmo report :
Once an electromagnet is attached to something, you cannot remove it again without a kerbal. Therefore, the magnet feature is no longer useful once it is attached via EVA. Is the method of attachment not magnetism? If not, what? Perhaps we need an option to fire a large solenoid from the center of the magnet and release the kerbal's chewing gum that's holding it in place?

Fixed in 0.4.2