I'd kinda suspected something like this was going on after seeing how the Map window was getting stuff inserted by the client.
I was dorking with the show_bag command a few weeks back and happened to toss a tooltip=parent.parent.name on the bag window close button just to see where the window was nested. Noticed the _HUD reference and decided to test general nesting at some point. A conversation with someone at SOE lead me to believe my suspicions were correct.
Took a while to get around to it, but I finally made a tester page with a buncha scripts to test various events related to Data Items, listbox, etc. Tossed in a series of buttons to grab the tree 5 levels out, then duped the entire test page and included it to every UI branch.
Once I confirmed everything was ending up under _HUD, I added a button to change the location of the Inventory window to a few of the other branch test pages and it worked
