There are two main ways to fail at the standards game: You can create software that handles documents in formats for which no true standards exist, or you can create a standard that exists only on paper and in committee, with no reference software implementation. Amazingly, for all its hype and bluster, with OOXML Microsoft has managed to do both.
I couldn't describe it better. OXML seems to be a dead standard at this point! Even if it it's no longer "MS OOXML" and is managed by ISO. In short: OOXML is defective by design