When using the new Search Engines Optimization features provided with SharePoint 2013 the browser title for the particular page will replace all contents of the PageTitlePlaceHolder Content Place Holder. This is important to know particularly when building hierarchical titles.
Hierarchical page titles are titles in the browser title bar that, next to the title of the current page, contain the name of the current section and the name of the website. Hierarchical titles make it easier for visitors and Internet search engines to discover where in the website’s structure the particular page is.
When using the new SharePoint 2013 SEO features the browser title for the particular page overwrites all contents of the PageTitlePlaceHolder which is usually used for writing out the page title. If you want to include other information you need to ensure that they are located in the Master Page outside the PageTitlePlaceHolder Content Place Holder for example:
<title> <asp:ContentPlaceHolder id="PlaceHolderPageTitle" runat="server" /> - <SharePoint:ProjectProperty Property="Title" runat="server" /> </title>