Content control distorts ReportViewer control

I have noticed that when I define a ReportViewer control within an <asp:Content>, its appearance is distorted. The ReportViewer is displayed like this:

It should look like this:

Does anyone know why this is happening? Right now, I put the ReportViewer on a page without a master page. I suppose that I could also create a custom master page and put the ReportViewer on it and everything else on the content page, although I have not tried it. Is there something else that I can do?
I am using VS2012 Express for Web and the Microsoft Report Viewer 2012 Runtime.