getElementByID01 expects find the specified node regardless of whether the
parser in validating or non-validating. 

From http://www.w3.org/TR/DOM-Level-2-Core/core.html#ID-getElBId

Note: The DOM implementation must have information that says which attributes
are of type ID. Attributes with the name "ID" are not of type ID unless so
defined. Implementations that do not know whether attributes are of type ID or
not are expected to return null.

This would definitely appear to allow non-validating parsers to return null. 
However, the wording may allow a non-validating parser to either return null or
a matching element since it might have read the DTD.

An additional test could be added where the attribute is named "id" and/or ID
but no DTD is specified.

Originally reported as part of bug 238