This looks like 3 separate problems:

1. Dragging an asset directly into the scene view (seems possible since 5.2) creates two copies of that asset in the project (repro in: 5.2 .. 5.5)

2. Dragging an asset to project view directly after opening the project makes the right-hand panel of project view disappear (it comes back when you select any project folder)

3. Dragging an existing project asset to its current location is not possible. This is clearly by design, but we can discuss if there is a need to change/improve this behaviour (since importing it using the context menu works fine).