Ondrej, this master page / page template uses HTML5.  Is there a way to instruct Kentico that it's an HTML5 website as opposed to an XHTML website?
Brenden, I created a simplified master page to demonstrate my problem.  Below is the .master file, the page template's .aspx file, and then what is actually rendered to a public/anonymous user.  The code-behind is empty aside from the boilerplate.
Here's the .master file:
<%@ Master Language="C#" AutoEventWireup="true" CodeBehind="DemoMasterPage.Master.cs" Inherits="CMSApp.CMSTemplates.DemoMasterPage" %>
<!DOCTYPE html>
<html>
    <head id="Head1" runat="server">
        <title id="Title1" runat="server"></title>
        <!-- <ltlTags> -->
            <asp:Literal ID="ltlTags" EnableViewState="false" runat="server" />
        <!-- </ltlTags> -->
    </head>
    <body class="<%=BodyClass%>" <%=BodyParameters%>>
        <form id="form1" runat="server">
            <asp:PlaceHolder ID="plcManagers" runat="server">
                <ajaxToolkit:ToolkitScriptManager ID="manScript" EnableViewState="false" ScriptMode="Release" runat="server" />
                <cms:CMSPortalManager ID="CMSPortalManager1" EnableViewState="false" runat="server" />
            </asp:PlaceHolder>
             <asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server">
            </asp:ContentPlaceHolder>
        </form>
    </body>
</html>
Here's the .aspx page template:
<%@ Page Title="" Language="C#" MasterPageFile="~/CMSTemplates/DemoMasterPage.Master" AutoEventWireup="true" CodeBehind="DemoPageTemplate.aspx.cs" Inherits="CMSApp.CMSTemplates.DemoPageTemplate" %>
<asp:Content ContentPlaceHolderID="ContentPlaceHolder1" runat="server">
    <p>Yo</p>
    <cms:CMSEditableRegion ID="MainContentEditableRegion" runat="server" DialogHeight="400" RegionType="HtmlEditor" RegionTitle="Main Content" />
</asp:Content>
And the actual, rendered HTML:
<!DOCTYPE html>
<html>
<head id="ctl00_Head1">
    <title>
        Our Site Title - Experiment
    </title>
    <!-- <ltlTags> -->
        <meta name="description" content="Our site description" />
        <meta http-equiv="content-type" content="text/html; charset=UTF-8" />
        <meta http-equiv="pragma" content="no-cache" />
        <meta http-equiv="content-style-type" content="text/css" />
        <meta http-equiv="content-script-type" content="text/javascript" />
        <link href="/CMSPages/GetResource.ashx?stylesheetname=OurStylesheetName" type="text/css" rel="stylesheet" />
    <!-- </ltlTags> -->
</head>
<body class="LTR Safari Chrome Safari37 Chrome37 ENUS ContentBody">
    <form method="post" action="/Experiment.aspx" id="aspnetForm">
        <div class="aspNetHidden">
            <input type="hidden" name="ctl00_manScript_HiddenField" id="ctl00_manScript_HiddenField" value="" />
            <input type="hidden" name="__EVENTTARGET" id="__EVENTTARGET" value="" />
            <input type="hidden" name="__EVENTARGUMENT" id="__EVENTARGUMENT" value="" />
            <input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE" value="/wEPDwUJNzkwOTkxMzYxDxYCHhNWYWxpZGF0ZVJlcXVlc3RNb2RlAgEWAmYPZBYEZg9kFgQCBA8WAh4EaHJlZgVaL0NNU1BhZ2VzL0dldFJlc291cmNlLmFzaHg/c3R5bGVzaGVldGZpbGU9L0FwcF9UaGVtZXMvTmV3NDIuTmV3VmljdG9yeS9kaWFsb2dQYWdlU3R5bGUuY3NzZAIFDxYCHwEFUC9DTVNQYWdlcy9HZXRSZXNvdXJjZS5hc2h4P3N0eWxlc2hlZXRmaWxlPS9BcHBfVGhlbWVzL05ldzQyLk5ld1ZpY3Rvcnkvc3R5bGUuY3NzZAIBDxYCHgZhY3Rpb24FEi9FeHBlcmltZW50LTIuYXNweGRkWNzrAIqAQhGN+utGjs7w7z2N4DZqgBpQECNkilwy0eA=" />
        </div>
        <script type="text/javascript">
            //<![CDATA[
            var theForm = document.forms['aspnetForm'];
            if (!theForm) {
                theForm = document.aspnetForm;
            }
            function __doPostBack(eventTarget, eventArgument) {
                if (!theForm.onsubmit || (theForm.onsubmit() != false)) {
                    theForm.__EVENTTARGET.value = eventTarget;
                    theForm.__EVENTARGUMENT.value = eventArgument;
                    theForm.submit();
                }
            }
            //]]>
        </script>
        <script src="/WebResource.axd?d=hrfs6WP0NHW3AiHRXbQJyGZU2bwz6nJetf2wwaqGQwclOyxdYZAp4SIr8uXJfUW9nEgtnTCDQBh5y7tCslCK1wI7QXZNw0GDrZ7gVWk60HU1&t=635200830466652144" type="text/javascript"></script>
        <input type="hidden" name="lng" id="lng" value="en-US" />
        <script type="text/javascript">
            //<![CDATA[
            function PM_Postback(param) { if (window.top.HideScreenLockWarningAndSync) { window.top.HideScreenLockWarningAndSync(1080); } if (window.CMSContentManager) { CMSContentManager.allowSubmit = true; }; __doPostBack('ctl00$CMSPortalManager1$am', param); }
            function PM_Callback(param, callback, ctx) { if (window.top.HideScreenLockWarningAndSync) { window.top.HideScreenLockWarningAndSync(1080); } if (window.CMSContentManager) { CMSContentManager.storeContentChangedStatus(); }; WebForm_DoCallback('ctl00$CMSPortalManager1$am', param, callback, ctx, null, true); }
            //]]>
        </script>
        <script src="/ScriptResource.axd?d=oDQsX_8uPIFwBmvp0DvFzvsybW20-DiXIPBCJW95W2Kupq6FRo0PNZ0WBh8pQrnUDFD5P8P8qLXTtxV483rwicvVdHJOudNIEV-HrtLb8Hs2MQInBi1lYlQuqdkCug0a0&t=7c776dc1" type="text/javascript"></script>
        <script src="/ScriptResource.axd?d=vINF2zKqmPYdQwoWkDoKl9DdgrcW2FR7UIr_72054hpsbKQc28bDdR15-u8A82bia6FHvUHh0LaFJ7aMO9WFIWXkVXlioi4L1qge3hyI6-n7PKmcB16-NYLuGu4lYcRT0uKxC6ZrQApXqAXF9CYHlQ2&t=7c776dc1" type="text/javascript"></script>
        <script type="text/javascript">
            //<![CDATA[
            var CMS = CMS || {};
            CMS.Application = {
                "isDialog": false,
                "applicationUrl": "/",
                "isRTL": "false",
                "imagesUrl": "/CMSPages/GetResource.ashx?image=%5bImages.zip%5d%2f"
            };
            //]]>
        </script>
        <script type="text/javascript">
            //<![CDATA[
            Sys.WebForms.PageRequestManager._initialize('ctl00$manScript', 'aspnetForm', ['tctl00$ctxM', ''], [], [], 90, 'ctl00');
            //]]>
        </script>
        <div id="ctl00_ctxM">
        </div>
        <p>Yo</p>
        <script type="text/javascript">
            //<![CDATA[
            (function () { var fn = function () { $get("ctl00_manScript_HiddenField").value = ''; Sys.Application.remove_init(fn); }; Sys.Application.add_init(fn); })();//]]>
        </script>
        <script type="text/javascript">
            //<![CDATA[
            if (typeof (Sys.Browser.WebKit) == 'undefined') {
                Sys.Browser.WebKit = {};
            }
            if (navigator.userAgent.indexOf('WebKit/') > -1) {
                Sys.Browser.agent = Sys.Browser.WebKit;
                Sys.Browser.version = parseFloat(navigator.userAgent.match(/WebKit\/(\d+(\.\d+)?)/)[1]);
                Sys.Browser.name = 'WebKit';
            }
            //]]>
        </script>
        <script type="text/javascript">
            //<![CDATA[
            WebForm_InitCallback();//]]>
        </script>
    </form>
</body>
</html>