Looks like URL resource type has several issues whith Display options. Moreover, display behavior sometimes is very different when accessing the URL form within the course home page and when using "Save and display", thus creating confusion to Teachers adding resources.

Examples:

• add an URL resource type, add an URL, say "http://www.mediatouch.it"
• set display option to automatic -> save and display -> on resource page appears a URL to click within Moodle interface
• set display option to automatic -> save and return to course -> click the URL resource ->the URL is displayed on the same window, loosing Moodle interface

• set display options to Embed -> save and display -> on resource page nothing displays except description
• set display options to Embed -> save and return to course -> click the URL resource -> on resource page nothing displays except description
  (coherent, but broken)

• set display options to Open-> save and display -> on resource page appears a URL to click within Moodle interface
• set display options to Open-> save and return to course -> click the URL resource -> the URL is displayed on the same window, loosing Moodle interface

Popup display seems working better, even if it has two different way to show when using "save and display" and when clicking the resource on the course home page.