Delete UI announces success immediately regardless of the actual result (for big terminal pages)

In order to reproduce:

• make a huge terminal page, with lots and lots of attachments , or otherwise prepare a terminal page that takes quite long to delete
• delete this page using the normal delete form
• the UI will immediately display success on delete: "The page has been deleted."
• however:
  • it is possible that the delete fails. In this case no error will be reported on the screen unless the page with delete result is reloaded
  • if the delete works fine, it's possible that it takes longer to finish, but the UI won't show it. In this case:
    • for a while after the launch of the delete the page will still be there, it can be accessed in a new tab, from the browser.

Expected result:

• if the delete fails, an error should be displayed on the screen
• if the delete does not fail, the delete UI should show that the operation is in progress for as long as the operation is not finished.

Otherwise put, the bug is that if the delete operation is not very fast (so that it can finish before the browser loads the second step of the delete UI), the UI always displays that the operation finished, and always with succes.