I have found some interesting behavior with push notifications on the Android Chatter App. If I create FeedItem where CreatedbyID = InsertedbyID then the push notification works for the parentID user but if CreatedbyID <> InsertedbyID, the notification does not post. See below the code I was using, if the senderId = logged in user it works.
FeedItem messages = new FeedItem();
Id senderId = '005i0000000DkTMAA0';
messages.parentId = '005i0000000EP95AAG';
messages.CreatedById = senderId;
messages.body = 'notify'));
Can we get it to fire when CreatedbyID <> InsertedbyID
Seems more like a bug to me but I will post it as an idea too.