Similar as extension, DOM UI needs to be created in its own process....

chrome/browser/tab_contents/render_view_host_manager.cc

Index: chrome/browser/tab_contents/render_view_host_manager.cc
===================================================================
--- chrome/browser/tab_contents/render_view_host_manager.cc	(revision 70598)
+++ chrome/browser/tab_contents/render_view_host_manager.cc	(working copy)
@@ -298,6 +298,12 @@
     // into the same process.
     if (new_entry->url().SchemeIs(chrome::kExtensionScheme))
       return true;
+    // When a tab is created, it starts as TYPE_NORMAL. If the new entry is a
+    // DOM UI page, it needs to be grouped with other DOM UI pages. This matches
+    // the logic when transitioning between DOM UI and normal pages.
+    Profile* profile = delegate_->GetControllerForRenderManager().profile();
+    if (DOMUIFactory::UseDOMUIForURL(profile, new_entry->url()))
+      return true;
     return false;
   }