INVALID_STATE_ERR or INVALID_ACCESS_ERR when attempting to write into XML documents

While reviewing the spec, we found the following apparent inconsistency and we'd like to understand the reasons for this:

In section 3.5.1/3.5.2 [1], Opening the input stream and Closing the input stream, the spec says to throw INVALID_STATE_ERR if the Document is an XML document.

In section 3.5.3/3.5.4, document.write and document.writeln, the spec says to throw INVALID_ACCESS_ERR if invoked on XML documents.

Is there a reason why these are different exceptions?

Many thanks,

Adrian.

[1] http://dev.w3.org/html5/spec/Overview.html#opening-the-input-stream