Microsoft's "Office Open XML" (or OOXML) family of formats which was approved as a standard by the ISO, albeit under controversial circumstances (using a ponzi scheme of promises to get skeptics to vote for it, most of which have not been fulfilled), is a classic case of a proprietary standard masquerading as an open standard - what some people refer to as a "fauxpen standard".
Microsoft has always held its proprietary control of the Microsoft Office file formats as its crucial competitive advantage - Bill Gates himself stated that if competing software products could reproduce Microsoft Office documents, it would be "suicide for our platform".
So, when a number of influential US states started making noise about mandating open standards compliance, rather than adopting the pre-existing, vendor-neutral, royalty-free Open Document Format (ODF) - already ratified as an open standard by the ISO - Microsoft created OOXML as a competing standard for its Microsoft Office software, using the complex standards process to obscure its effective unilateral control of the so-called open standard.
When the UK government undertook its public consultation process regarding the adoption of open standards for government software and collaboration with the public, it considered both ODF and OOXML, but, despite substantial pressure from Microsoft, they selected only one open standard: ODF.
According to the minutes of meetings of the Technical Standards Panel who advised the Cabinet Office:
"The chair asked LH [Linda Humphries, open standards lead at the Government Digital Service] to explain why ODF was chosen rather than another format such as Office Open XML, also known as OOXML,” said the minutes."
“LH explained that the decision was based on the Open Standards Principles and the UK government definition of an open standard. Both ODF and OOXML, were considered but ODF better met the criteria."
“For OOXML, there were concerns relating to the vendor independence and market support criteria - particularly with differences between transitional OOXML and strict OOXML conformity.”
The stakes were so high in this UK decision, that Microsoft lobbyists have subsequently been accused of threatening MPs with job losses and other threats. Even so, the UK government went ahead with the policy change to mandate the use of ODF over OOXML because, according to Steve Hilton, former Conservative party strategy chief, "it's the right thing to do."
Sadly, as we are sure Microsoft knows, many other governments will not investigate the "nuances" of this situation and will take MS' assertions - that its products adhere to "open standards" - at face value.
More-over, some governments will also fall for Microsoft's favourite gambit: "it's great to have a choice of open standards". No. The idea of multiple standards covering the same functional domain is entirely wasteful and counterproductive. It's like saying: "ok, we have the Metric System, but in interest of 'choice', let's also introduce Imperial Units as an acceptable standard for measurement..."
Update 2015-10-07: The government of the Netherlands has announced that it will be shifting to ODF and will cease to accept OOXML as an open standard.