Xpath query unexpectedly returns 0 in Java/groovy, works in other interpreter

I'm trying to create a Cucumber step definition in Groovy that finds a certain node in an XML document (a Solr search result) by the value of a mandatory 'url' tag and returns this node's position in the list of results.

This is my step definition:

Then(~'^I will see the position of this url: "([^"]*)"$') { String text -> 

    pageSource = browser.getPageSource()

    //Prints the position of the relevant search result
    def xpathString = "count(/response/result/doc/str[.='" + text + "']/parent::*/preceding-sibling::*)"  //+1

    builder = DocumentBuilderFactory.newInstance().newDocumentBuilder()
    doc = builder.parse(new InputSource(new ByteArrayInputStream(pageSource.getBytes("utf-8"))))
    expr = XPathFactory.newInstance().newXPath().compile(xpathString)
    posisjon = expr.evaluate(doc)
    println "The position of this result is: " + posisjon.toString()
    println xpathString

}

Here's an example of the XML result I'm evaluating:

<response>
    <lst name="responseHeader">
        <int name="status">0</int>
        <int name="QTime">75</int>
        <lst name="params">
            <str name="indent">true</str>
            <str name="q">pris</str>
            <str name="wt">xml</str>
        </lst>
    </lst>
    <result name="response" numFound="306" start="0">
        <doc>
            <str name="url">/nasjonalregnskap/nokkeltall/priser-og-prisindekser</str>
            <str name="id">3730</str>
            <str name="tittel">Priser og prisindekser</str>
            <str name="innholdstype">nokkeltallsside</str>
            <date name="publiseringsdato">2010-11-23T11:35:00Z</date>
            <str name="hovedemner">Nasjonalregnskap</str>
            <str name="sprak">no</str>
            <str name="rom">statistikk</str>
        </doc>
        <doc>
            <str name="url">/7292/pris-forbruk-og-inntekt</str>
            <str name="id">7292</str>
            <str name="tittel">Pris, forbruk og inntekt</str>
            <str name="innholdstype">publikasjon</str>
            <date name="publiseringsdato">2002-06-13T10:00:00Z</date>
            <str name="hovedemner">Befolkning</str>
            <str name="sprak">no</str>
            <str name="rom">statistikk</str>
        </doc>
    </result>
</response>

However, when I run this test (we're using Maven to build and run, so I have limited debugging options afaik) I get this output from the two println commands:

The position of this result is: 0

count(/response/result/doc/str[.='/7292/pris-forbruk-og-inntekt?fane=om']/parent::/preceding-sibling::)

However, when I evaluate this Xpath query to the exact same XML document in Altova XMLspy, I get the expected result!

Apparently I don't have enough reputation (sorry, sorry...) to post images, here's a link to a screenshot of the result in Altova XMLspy

So the question I can't figure out is: Does the Java XPathFactory evaluate xpath differently from other interpreters? Have I made a mistake or error in my implementation? The answer eludes me :)