JRexHTMLFrameElementImpl.getContentDocument() returning wrong Document?

I'm observing some unexpected behavior when processing HTML frames.  

Let's say I have a web page frameset.html, and it contains one frameset.  Let's
say the frameset consists of two frames, one defined by frameA.html and the
other defined by frameB.html.  Now let's say I open frameset.html in JRex to
obtain the Document object for frameset.html, which in turn I use to get a
reference to the HTMLFrameElement object for the frame tag representing
frameA.html:  


NodeList frameNodes = doc.getElementsByTagName("frame");
HTMLFrameElement frameA = (HTMLFrameElement)frameNodes.item(0);
                    

According to
http://jrex.mozdev.org/docs/api/org/w3c/dom/html2/HTMLFrameElement.html, the
getContentDocument() method of the HTMLFrameElement should return the Document
contained by the frame.  I interpret that to mean that when I call
frameA.getContentDocument(), I should get a Document object representing
frameA.html.  Instead, I get what appears to be another Document object
representing frameset.html.  

Am I misunderstanding the intent of getContentDocument()?  Or am I wrong in
concluding that getContentDocument() is returning another Document that
represents frameset.html?  Or is this a bug? 

Thanks,
Matt