I regularly use a website in which a submit button does not change state in any way. It is indistinguishable from the click having gone to /dev/null. And the completion of the action takes a copule of seconds.

In the good old days, you'd have the request sent by that button reveal a small, transient status bar showing the target URL at the bottom, plus the "Refresh" button in the browser toolbar would change to "Stop" instead; both effects lasted for the duration of the network roundtrip. It was enough of an indicator, and since it was not controlled by the website, it wouldn't break or lie to you.