I noticed that three items I had moved from one document to another are back in the original document.
Two of the items I had also changed the name of, and they reverted to the previous name as well.
Each of them were moved from one document in outline pane without grouping, to another document of the same kind. I used the click/drag method to hold the item, move it to another pane which had the other document open, and then under the item I wanted it to be under.