XMLPlugin XercesParserImpl.endElement() invalid prefix

relax-ng branch.
I am trying to use http://www.w3.org/2007/schema-for-xslt20.xsd.
elements taken from this schema show up with an extra : in the completion list, e.g. xsl::for-each
I have traced this to XercesParserImpl.endElement()
//get the prefix
String prefix=qName.substring(0,qName.length()-sName.length());
gets the prefix and the following :
It should be something like:
String prefix;
if (qName.length() == sName.length())
prefix = "";
else
prefix=qName.substring(0,qName.length()-sName.length()-1);