This has happened in some variety in previous iterations of Acrobat; I went into organize pages and after the first reorder (I dragged page 5 into position 2) 4 pages appeared from a document I had created yesterday. I did no functions to import any items to the current document. I only wanted to delete 2 pages (starting # 2 and 3) and move the last page to be page 2 instead of page 5. The pdf that was inserted into my document wasn't even open.