Never been a fan of iTunes. Hit & Miss is situations like yours.
The ones that are saving as Word docs; can you check the file extension (the last letters after the full stop, i.e U2.mp3 or U2.m4a) To if you can only see the name of the file then do the following , from the Menu Bar of Explorer (File, Edit, View Tools, Help), click the tools button, then click folder options, then click view, then scoll down the list & make sure
that the 'hide extention for known file types is unticked . It may be the wrong file extention is causing the problem which would identify the file incorrectly to Windows & iTunes.