It seems a trifle odd that Microsoft would join a group working on the OpenDocument standard since it has its own rival standard, Open XML, and consequently, the OpenDocument partisans are suspicious. Ingrid Marson explains at CNET:
Microsoft has joined a committee that has a key role in the ratification of the OpenDocument format as an international standard.
Microsoft asked to join the INCITS/V1 Technical Committee on March 15. This committee is responsible for reconciling the votes that are cast by the International Organization for Standardization (ISO) over the acceptance of the OpenDocument format.
Pamela Jones, who runs legal Web site Groklaw, speculated that Microsoft may have joined the group to sabotage the ratification of ODF, hoping to give its rival standard a chance to catch up. Last year, Microsoft submitted its Office Open XML file formats to European standards body ECMA International, as a prelude to seeking ISO standardization later.