Steps to reproduce:

1. Open two instances of Unity with different projects (Can be newly created)
2. From one Unity instance drag any GameObject or Prefab onto Scene view of another Unity instance.
3. Check the console.

Expected result: Empty.
Actual result: Error message appears.

NullReferenceException: Object reference not set to an instance of an object
UnityEditor.SpriteUtility.GenerateDefaultSprite (UnityEngine.Texture2D texture)

Notes:
On 5.40b10 always reproduces.
On 5.3.4f1 sometimes does not reproduce.
On 5.2.4f1 does not reproduce at all.

Regression from 5.2.4f1.