OK, I finally got it. What I did that helped was that instead of keeping ‘My Computer’ open in windows explorer, I opened any other folder and set the left side to show folders and made sure computer was expanded there instead. (I suspected the regular behavior windows explorer would try to ‘read’ the DFU device which was confusing the thing and triggering the disconnect/reconnect behavior)
At that point I could see the DFU device connect without it immediately vanishing, copied the P2 over and it took in one shot.
SW