I have this issue when using servers with a fancy authentication schema, in some special editing situations (long edits, restarts during the edits, authentication loss, etc).
Sometimes when hitting "save and continue" the UI displays success while the save doesn't actually happen.
I investigated and this happens when the actual request to save makes a redirect to a page that returns the HTTP 200 code. The actual JSON that a successful save returns is not contained in this response, but apparently this doesn't prevent the UI from displaying success. Other HTTP codes are properly handled (namely 401, 403 or XHR errors - which take place in some authentication cases), but not the 200.
In these cases, the user may close the window or hit cancel believing that their content was actually saved when nothing actually happened.