[Newbie] Pipeline to store the input file fails; what am I doing wrong please?

Hi Folks, 

This pipeline stores the input document Bookstore.xml into a file
test.xml:

-------------------------------------------------------
<p:declare-step xmlns:p="http://www.w3.org/ns/xproc" 
                name="myPipeline">
    <p:input port="source">
        <p:document href="Bookstore.xml"/>
    </p:input>
    <p:output port="result">
        <p:pipe step="step1" port="result"/>
    </p:output>
    
    <p:store href="test.xml" name="step1"/>
</p:declare-step>
-------------------------------------------------------

What am I doing wrong please? 

Error message I get using Calabash 0.8.5:

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Error  : Pipeline failed: 
com.xmlcalabash.core.XProcException:
net.sf.saxon.s9api.SaxonApiException: 

Supplied XPathVariable is bound to the wrong slot: 
Perhaps it was created using a different static context

com.xmlcalabash.core.XProcException: 
net.sf.saxon.s9api.SaxonApiException: 

Supplied XPathVariable is bound to the wrong slot: perhaps it was
created using a different static context
        at
com.xmlcalabash.runtime.XAtomicStep.evaluateXPath(XAtomicStep.java:560)
...
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/Roger