Hmm, I very much doubt the XLSX format is wrong. It's being used successfully everyday by hundreds of thousands of people, perhaps more. My take is that you must have misunderstood part of it.
Comment on Re: The XLSX Perl modules have a simple problem
I haven't read the file format specifications, so I am not making any claims about standard compliance. I do see an increasing number of files uploaded by users, mainly from Russia, where the Perl modules fail because of this small problem.