Hello Rieni De Rijke,
We have this item logged in our backlog, but it is with relatively low priority since the validation errors don't cause critical issues like crashes or inability to show the document.
About the OpenXML version which we are using - when we implement new features and make the related import/export functionality available, we always use the newest available specification. This means that more than one version is used for RadRichTextBox's DocxFormatProvider and we cannot claim that any specific one is used.
If you have further questions, I'll be glad to assist you.
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