panels_node_form() cannot be submitted programmatically if the node is new

When building the form, panels_node_form looks for $node->panel_layout . If that's not set (for example when creating a new node) then it looks to arg(3) to see if the panel layout is specified there. If it's not there, drupal_goto bounces you back to layout selection.

This is a problem when trying to deal with new panel nodes programmatically, since the URL will not be of the form panels_node_form is looking for and, rather than build the form, it'll drupal_goto to layout selection.

I am personally running into this when using panels_node together with hierarchical_select.module. HS allows for ajax-based widgets for drilling down into hierarchical taxonomies. If I try to drill down while creating a new panel node, hierarchical_select calls a function which attempts to build the panel node form again and return deeper part of the hierarchy via JSON. But, since the path which invokes that function (/hierarchical_select_json) doesn't meet the criteria above and so drupal_goto takes you to layout selection. Since the response is now HTML and not JSON, hierarchical select fails.

I tested this with a bare installation, only non-core modules installed were hierarchical_select, ctools, and panels.

Let me know if I can provide any more info. I'm happy to write the patch myself given a bit of direction but I don't want to go in a direction that doesn't make sense to the maintainers.