When charging is not connected, sliding fingertip is smooth without any resistance.
When sliding finger while touching the body with finger of the other hand - the slide is smooth as well. When released the "resistance" comes back.
I've noticed this with one of my old macbook pro from couple of years ago as well.
Is this normal? Is it safe? Is it "just" grounding issue? Can I somehow ground body or should I double check grounding on my power supply?