If two or more users have a document selected, an action performed by one user will be overridden by the actions of the second user.
Actions include; adding a note, changing the file name, deleting a document and re-indexing.
You may have the scenario where two users are looking at the same document. The first user deletes the document. The second user, re-indexes the document to a different cabinet. These actions happen at almost exactly the same time. The last action is the re-index. So rather than the document being moved to Deleted Items (as the first user would expect). It ends up where the second user was re-indexing it to.
Another scenario may be if two users have selected the same document and are both adding a note. Whatever information the first user has added will get replaced when the second user saves their note. This also applies to changing a file name and index values.