gistfile1.js

var pageCount = 3;
var thumbnails = {
  1: "http://s3.documentcloud.org/documents/8941/pages/fbi-agent-william-h-lawrence-testifies-before-congress-p1-thumbnail.gif",
  2: "http://s3.documentcloud.org/documents/8941/pages/fbi-agent-william-h-lawrence-testifies-before-congress-p2-thumbnail.gif",
  3: "http://s3.documentcloud.org/documents/8941/pages/fbi-agent-william-h-lawrence-testifies-before-congress-p3-thumbnail.gif"
};

var thumbnailsHTML = JST.thumbnails({
  pageCount : pageCount,
  thumbnails : thumbnails
});

gistfile2.erb

// thumbnails.JST - BROKEN

<%= pageCount %>
<%= thumbnails[pageCount] %>
<% _.each(thumbnails, function(p) { %>
  <div class="DV-thumbnail">
    <img src="<%= p %>" />
  </div>
<% }); %>

gistfile3.erb

// thumbnails.JST - WORKS OK

<%= pageCount %>
<%= thumbnails[pageCount] %>
<% _.each(thumbnails, function(t) { %>
  <div class="DV-thumbnail">
    <img src="<%= t %>" />
  </div>
<% }); %>