I was merging several documents together that were all formatted identically (same font, same bullets, same margins). The merged documents are riddled with errors. Bullets have moved or changed type. Pagination has changed. Sentences that should have been in normal text are underlined, in bold, or italics (or all three). Some paragraphs are double spaced and have 6 point spaces after each line. What causes this and what can be done to make sure it doesn't happen again?