Steps to reproduce:
At this point you will notice some text at the top left corner of the document.
The problem is this:
<!-- page content including button to open dialog -->
<!-- dialog content -->
This text does not belong to any page
but it will show up on the background
of the dialog
hmmm not really sure this is a bug. the content is there why would it not be shown? @uGoMobi thoughts?
We set background none for dialogs because we want to show the overlay (page container). That's why you see other content that is not wrapped in a page.
When we switch from dialog as a widget to an option in the page widget we could consider setting the overlay theme on the page if it is a dialog. However, I think it's the dev's responsibility to handle content (other than widgets like panels and popups) outside pages when using pages.
So I consider this not a bug so I am closing the ticket. If possible we improve this when making changes to dialog for 1.5.