Reproduction steps:
1. Open attached project
2. Drag "bubble10" sprite into scene view, but drop it in restricted area (like console dock, gif included)

Expected behaviour: Object does not get instantiated into the scene
Actual behaviour: A unreferenced object gets instantiated. It cannot be selected/moved

Regression introduced in: 2017.1.0a4

Reproduced on: 2017.1.0a4, 2017.1.0b2, 2017.1.0b3
Not reproduced on: 5.6.0p3, 2017.1.0a3

Note:
Reproducible on both, Mac and Windows with any draggable object