Steps to reproduce:
1. Build a new project
2. Run the game
3. Select input tab
4. Double click on any entry to change it

Expected Results:
Pressing a button/key is accepted

Actual Result:
No matter what key/button is pressed, the inputs is not recognised and the "Press the button or key for..." dialog is displayed. It never goes away, you cannot escape it or select any other option or button, leaving you to Force Quit the game.

Reproduced in: 2017.1.0b6, 5.6.1f1, 5.6.0b1
Not reproduced in: 5.6.0a6, 5.5.3p3
Regression since: 5.6.0b1
Reproduced using macOS Sierra 10.12.4