1. Open scene "mainScene"
2. Select any button from withing scene view
3. Change "Graphic" for the selected button from inspector
4. Scroll through the list with arrow keys up and down (so it would select all elements while doing so)

Actual result: UI elements disappear (See video in first edit)
Expected result: They do not disappear

Possible workaround: Play scene, and it all resets

Tested and reproduced on:
Windows 10
Unity 5.4.0b8

Cannot test in 5.3 due to bug 744044

NOT Reproducible in:
Unity 5.1.4f1, 5.2.4p1