There is no obvious control to save changes on the settings page. If there is it should be “louder”.
Are you referring to an app or the website? This doesn’t sound like a bug.
I feel it is a bug (page design) even if there is a control as it is not obvious. It is a usability bug at the very least.
The save changes button is at the bottom of the page.
Since there are plans to redesign the account settings page at some point, I’m going to close this request.