Re: Fail safe?
Buttons that don’t click when you press them are a horrendous UI failure. You see the problem with slow user interfaces - people naturally click again and the second click can be on something behind a modal - fail.
You can fade-in the button, or grey out the button while it is disabled, but those solutions also lead to unwanted side-effects.
Pop up modals and unexpected scrolling are hard problems (on Android Chrome double clicking an input box selects, but the first click pops up the keyboard and scrolls the input box away, very annoying!)