SOAP addComment method does not accept URLs using SOAP::Lite

The addComment method appears to work for most comment content, but not URLs. I've been trying to determine why, but I just don't have enough information about how this works.

If I include a comment:
--SNIP--
This is a link to:
slashdot.org
--SNIP--

JIRA adds this fine, but if I include a comment:
--SNIP--
This is a link to:
http://slashdot.org
--SNIP--

JIRA returns a 500 with the following fault information:
--SNIP--
<?xml version="1.0" encoding="utf-8"?><soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"><soapenv:Body><soapenv:Fault><faultcode>soapenv:Server.userException</faultcode><faultstring>org.apache.axis.types.URI$MalformedURIException: The scheme is not conformant.</faultstring><detail><faultData xsi:type="ns1:URI$MalformedURIException" xmlns:ns1="http://types.axis.apache.org"/><ns2:hostname xmlns:ns2="http://xml.apache.org/axis/">[internal hostname removed]</ns2:hostname></detail></soapenv:Fault></soapenv:Body></soapenv:Envelope>
--SNIP--

It is an xs:string field, so I don't understand why having a URL scheme in the content makes any difference. If I had a full stack trace and the code I'd look it up myself, but I don't even see a stack trace in any of the jira logs on the filesystem.

I'd like to have the fully-qualified URL in the comment so users can click on it, but I don't know how to make it work. I tried wrapping it in [CDATA[]], but that was no help. I tried URL-encoding it, but it was not URL-unencoded on the other end. I'm out of ideas.