'Panel title' pane is empty after saving page with IPE

This is a known deficiency in the IPE right now. Certain bits of content are filled in via hook_preprocess_page and that does not get run when IPE updates a page. This is, I agree, very annoying, but it's not completely critical and so I haven't prioritized it as something to devote time to trying to resolve.

The short version of what needs to happen is that we need to run CTools' token substitution system over the output before it is sent back, but that more or less means running a theme('page') so we can get that data, and then not actually using the output because we don't actually want to theme('page') it. That makes things...tricky.

I've been trying to track this one down also and assuming this is all related; in our case we are also losing our Main Menu tree (in addition to our custom Page Title) on every "Save" after customizing a page. I originally assumed this was Panelizer/IPE bug but after disabling Panelizer I can easily duplicate using a plain Panel page and IPE:

1. Create a panel page with a simple Menu Tree block, a custom Page Title, and of course a Body field and some other random panes

2. On first save, everything appears normally

3. If you then "Customize this page" and "Save", both the Main Menu Tree and the custom Page Title disappear (other fields, such as body/custom render normally)

4. Refresh, and everything re-appears as it should

Not sure if it helps but here are the somewhat related tickets I've tracked down, some have been marked as "fixed" but seem to be dealing with the same/similar issue:

"Menus disappear when saving in IPE, page refresh needed to bring back." (Open in Panelizer queue, but not really a Panelizer issue)
http://drupal.org/node/1835456

"Panels IPE Save Drops Context Specified in Page Manager" (Marked as fixed)
http://drupal.org/node/1772834

"Panelizer default content and IPE, without page refresh panel is emptied on second save" (Marked as fixed, Panelizer queue)
http://drupal.org/node/1572202

Also related #1780742: Panelizer (Full Page Override) + Page Elements (eg: page_tabs, page_title) break Panels IPE

Tagging for easy reference.

See #2824874-2: Fake path for better context when rendering panes with IPE which fakes the path to provide better context when rendering panes.

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