Bug ? Can not swich page type when restricted

<%- if @topic_view.topic.tags.present? %>
<%= t 'js.tagging.tags' %>: <%- @topic_view.topic.tags.each do |t| %> <%= t %> <%- end %>
<% end %>

** Silver striped version: 4.8

So in my tree I have a news group.

class News extends page {
      private static $allowed_children = array ('Recent', 'Old');
}

Without problem, I can only create a Recent or Old page type inside.
But it seems impossible to switch from Recent to Old for example.

I get an error message like [ The page type “Page” cannot be created under this page ] when I am not using Page, I am just switching from Recent to Old.