Destiny Player Support have put up a #Help article explaining how to avoid losing items that remain on the ground. They recommend always going to Orbit when you finish an activity rather than closing the application, switching characters, or powering off your console. For the full details you can read the [url=https://www.bungie.net/en/Help/Article/13965]article here[/url].
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#Destiny
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Yep I found several items in my mailbox that fell off the map, it was a welcome surprise.