Drag-and-drop multiple items onto a List in the Inspector works fine for items of the proper type but doesn't work properly for items with a Component of the proper type.

2) How can we reproduce it using the example you attached.
1. Open __Prospector_Scene_0

2. Select _MainCamera in the Hierarchy.

3. Lock the Inspector on _MainCamera by clicking the lock at the top, right of the Inspector.

4. Drag _Sprites/Spade onto the suitSpade variable of the Deck (Script) Component. This demonstrates that Unity will dig into the Spade Texture2D to find the Sprite underneath and assign it properly to the variable.

5. Click the disclosure triangle next to Letters in the _Sprites folder of the Project pane. Select the Letters_0 Sprite in the Project pane. Shift-click Letters_15 to select all 16 Sprites of Letters. Drag all of them over to the rankSprites variable of Deck (Script). This demonstrates that Unity correctly assigns a group of selected Sprites to a List of Sprites.

6. Select FaceCard_11C in the Project pane. Shift-click FaceCard_13S to select all 12 face card Texture2Ds. Drag this over to the faceSprites variable of Deck (Script). faceSprites does not open correctly, and the (+) icon is not displayed. None of the Sprites under the group of Texture2Ds are assigned to faceSprites.

7. Disclose the triangle next to faceSprites in Deck (Script) and set its size to 12.

8. Select the group of FaceCard Texture2Ds again and drag them into Element 0 of faceSprites. Now, one of the Sprites in the group is assigned to Element 0, but none of the others are assigned.