SonicStage CP 4 lets you copy and play tracks from one PC to another

Here's a strange thing.

I've got a desktop PC at home that I use to synchronise music to my NW-A3000 Walkman using SonicStage CP v4. I've been ripping to ATRAC 160kbps with High Recording Quality and Add Copy Protection unchecked.

I discovered yesterday that I could open up SonicStage CP4 on a different PC and drag these ATRAC tracks from the device to My Library and they played back with no DRM blocking. MP3's on the NW-A3000 couldn't be dragged over, just the ATRACs.