Feed items can be published multiple times if updated rapidly

Sometimes an item is imported & auto-published, then a content editor might decide to un-publish the node. Sometimes items are getting auto-published again.

One possible scenario: If a feed item is flagged for auto publishing (added to the feeds_publish_map table) and then the feed item is updated before feeds_publish processes the node, it could be selected a second time and the module will attempt to add it to the mapping/queue again.