Peculiar behavior of addHeader

[Kent Tong]

Hi,
I'm studying the security example in Axis 1.1, in particular the
SignedSOAPEnvelope class. To sign a message, it needs to add
a header:
        SOAPEnvelope env;
        ...
        SOAPHeaderElement header =
                new SOAPHeaderElement(
                XMLUtils.StringToElement(SOAPSECNS, "Signature", ""));
        env.addHeader(header);
If I change it to:
        SOAPEnvelope env;
        ...
        SOAPHeaderElement header =
                new SOAPHeaderElement(SOAPSECNS, "Signature");
        env.addHeader(header);
It also runs, but the signature element generated as an extra
"mustUnderstand" attribute:
<soapenv:Envelope
        soapenv:actor="some-uri" soapenv:mustUnderstand="1" ...>
        <soapenv:Header>
                <SOAP-SEC:Signature soapenv:mustUnderstand="0">
                ...
But this doesn't happen if XMLUtils.StringToElement is used:
<soapenv:Envelope
        soapenv:actor="some-uri" soapenv:mustUnderstand="1" ...>
        <soapenv:Header>
                <SOAP-SEC:Signature>
                ...
Why is that so?
Thanks in advance!