Reproduction steps:
1. Open the attached project 776325
2. Open scene "scene"
3. Try to select any object by clicking on them in the Scene view
4. Now try to select object by click-and-dragging

Expected behavior: it should be possible to select objects in the scene view by clicking on them.
Actual behavior: cannot select by clicking on an object in the scene view when script is running.

Reproduced on: 5.4.0b9, 5.3.3p2, 5.2.4f1