Slide disappearing in Beamer with beamerdefaultoverlayspecification{}

I have the following slide. beamerdefaultoverlayspecification{<+->} is used in the document.

begin{frame}frametitle{The problem}
  begin{itemize}
  item First item
  item Second item
    begin{quote}
      uncover<2>{
      ``A quote illustrating the second item that I want to reveal together with that item.''
      }
    end{quote}
  end{itemize}
end{frame}

As it says, I want to reveal the quote at the same time as the second item is revealed. If I don’t put in the uncover, the quote is revealed in a separate step. But if I do put it in, then the quote is not displayed at all. (Text added after the itemize environment is still displayed, it’s only the quote the disappears.)

The problem can be solved in this inelegant way:

begin{frame}frametitle{The problem}
  begin{itemize}
  item First item
  item<2> Second item
    begin{quote}
      uncover<2>{
      ``A quote illustrating the second item that I want to reveal together with that item.''
      }
    end{quote}
  end{itemize}
end{frame}

Can anyone explain what’s happening here? Why does the quote disappear? Why is the <2> necessary?

begin{quote}<2>
  % <your quote>
end{quote}