URLTag defines property encodeResult:

protected boolean encodeResult = true;

public void setEncodeResult(boolean encodeResult) {
    this.encodeResult = encodeResult;
}

But the corresponding tld entry is
<attribute>
    <name>encode</name>
    <required>false</required>
    <rtexprvalue>false</rtexprvalue>
</attribute>

Should be changed to <name>encodeResult</name>.

BTW: After one year of extensively using xdoclet for our custom tag libraries, I cannot understand why even "xdoclet haters" do not use it for tld generation.
Between the TagClass and the tld file is, in terms of ER, a strong relation, so that manually maintaining updates on both is real redundant. If using xdoclet, your tag class is the lead - no need to keep up tld yourself. Even documentation of the Tags can be edited at one single place (not to mention that current ww2 tld has no doc at all).
Second big advantage is that you can really use inheritance in tags, extending existing taglibs with custom tags without having to rewrite tld, or better, keep up with it yourself.

Rainer Hermanns and me could do the whole work on this task if someone would let us ;-)