Cannot change controller mappings on Configuration > Input

[Vanessa Faxanadu]

it seems like it pops up a dialog that says (possibly) to press a key with a time delay, but doesn't allow to press a key or a controller button, right after the UI button is clicked on the GUI to change either the "Up" (U), "Down" (D), "Left" (L), "RIght" (R), Select, Start, B, or A buttons, it disappears as quickly as it is pressed.

I have a third-party Xbox 360 wired controller, and it even does it when I attempt to do it with a keyboard.

Ubuntu Version, as reported by `lsb_release -rd`:
Description: Ubuntu 14.04.2 LTS
Release: 14.04

nestopia version: 1.45+dfsg-1

Expected:
To press a keyboard key or controller button to map to a virtual NES controller

What happened instead:
Dialog or whatever it was quickly disappeared without allowing the expected behavior, as described above, to happen.