If you click and drag a component in the Desktop preview iFrame and drop it in the Mobile preview iFrame it currently removes the component from Desktop and shows it where you dropped it in the Mobile view. This should not be possible.
When dragging starts in a iFrame, the other iFrame(s) should be greyed out so that the user cannot drop the component into them.
Closed: duplicate
Page builder
This is a duplicate of 🐛 Block dragging components from the desktop view to the mobile view Needs review .
Transferring credit.