There could be a mix up between the global and site-specific settings. When you are looking at the "page title format" setting, check the dropdown in the upper left corner of the page. There should be global settings as well as site-specific settings which if set, override the global settings for that site.
Another problem could be that an ancestor page is overriding the Title metadata setting. Each new child page will by default inherit the parent. You need to be sure that all ancestors have blank page title settings, too.