Sebastian Fiedler and Tom Clifton both wrote to the Manila-Dev list today about what sounded like a bug in Manila’s implementation of the Content Editor editorial role, as applied to News Items. Apparently Content Editors were not allowed to create or edit News Items, even if the preferences on the News Items prefs page were set to "All Editors".
I checked the docs which say, "The Content Editor can edit all the stories, pictures, and messages on a site like a Managing Editor but can’t edit templates and set the various site preferences." It sounded like Content Editors should be able to create and edit News Items, so I did some digging.
It turned out that this was a bug. When the Content Editor role was implemented, a couple of key scripts having to do with News Items had been missed. A fix was just released through root updates. Update Manila.root to get the changes.