To recreate this problem, install panels 3.3 and the latest dev release of Secure Pages. Enable the node template panel, add a variant for a content type, add a field from that entity, and try to edit the style. It will fail with:
An AJAX HTTP request terminated abnormally. Debugging information follows. Path: http://foo.bar.com/ttps%3A//foo.bar.com/panels/ajax/editor/style-settings/panel_context%253Anode_view%253Anode_view_panel_context_3/region/center StatusText: ResponseText: ReadyState: 4
Basically any form action that is set to an absolute URL in the panels code will cause this response.
There are six places in the Panels code where an absolute URL is used for the form action. There are plenty more where a relative URL is used. Is there a reason to use an absolute URL in some places? For example, if the Panels code is changed to use relative URL on the styles setting form, then the URL is not malformed and Panels appears to work properly.
Granted this behavior is due to interplay with Secure Pages module (and there is a bug in its url altering code that is triggered because of the absolute URL), my question is whether there is a design reason to use an absolute URL in Panels. The absolute URL is not ubiquitous in the Panels code and does not seem to be needed based on my observations.
Remove the code creating an absolute URL. See the patch.
User interface changes