For example I have a file with filename "$16,949.mobi". The tags shown in mobipocket are Title:"$16,949" and the Author:"Larry Niven".
When I add the file in Calibre the author becomes "harry" and the title stays correct. In another file I get the title to display the author and the author shows as unknown. In another file I get everything correct. I another I get the title correct and the author gets a name of another author from other books. If it helps, these are similar errors that I got when I was converting the books from text to mobi with the mobi reader. Sometimes after importing a book I would get for example the name harry as the author, but I have corrected all the books one by one in mobi reader. Now it seems as if Calibre displays the original tag data and not the corrected ones.