Content Place Holders don't migrate to nested master page

I inherited a project which, in my opinion, misused or overused the concept of the ContentPlaceHolder. They even put CPHs within the Head section, which I thought was rather weird.
Bottom line is that I need to create a nested master page from the first one, but when I attempt this, only five of the thirteen Content Place Holders migrate down to the nested master page as Content tags. I noticed that the eight CPHs that don't migrate down to the nested MP are contained within div tags. Whenever I've used CPHs, I've always used div tags within the CPHs. Any opinions on this subject? Should I work to reposition the div tags inside of the CPHs? See code below.
<%@ Master Language="C#" AutoEventWireup="true" CodeFile="~/masters/frontend.master.cs" Inherits="frontend" %> <!DOCTYPE html> <html xmlns="http://www.w3.org/1999/xhtml" runat="server" id="htmlEntity" ...