This is actually a misunderstanding of how it works. Some explanation:

- Palette only has Tiles, never Sprites or Textures
- If you drag in Sprite or Texture, a new Tile asset is generated. You get to choose the save path in a dialog.
- Palette can have the same tile multiple times.

What happens in the video:
1. You have an existing tile (A) in the palette
2. You drag in a sprite
3. Unity wants to generate new Tile (B) based on your Sprite
4. For your new Tile (B), you choose the path of an already existing Tile (A)
(5. All existing references to old tile (A) seem to break, but a ghosts still persists.)

I think the step #5 reveals a bug about how tilemap doesn't handle missing references optimally, but we will make a new fogbugz for that.