pls check my version http://halejcio.com/SimpleXLSX.zip,
i had problems with xlsx files from libreOffice, class doesnt work properly.
so....i made little changes.
(oreginal file)line: 298 main problem was somewhere here, with unpacking,
but your code was too smart for me :)
so i replaced it using simpler method with zip_open,etc. now it works fine for me. but im not sure is that ok for every case, so pls take a look on it.
(oreginal file)line: 477 libreoffice sheets starts counting from 2,
change: i cut off number from sheet name (sheet1.xml=>1), and use it as id in table, in libreOffice, first rId is file: style.xml, not sheet.
if u dont understand my english just check class with xlsx from libreOffice :)