calabash: p:identity with multiple inline

take

 <p:pipeline name="pipeline"
            xmlns:p="http://www.w3.org/ns/xproc">

   <p:identity name="step1">
        <p:input port="source">
              <p:inline>
                  <root1/>
              </p:inline>
              <p:inline>
                  <root2/>
              </p:inline>
              <p:inline>
                  <root3/>
              </p:inline>
              <p:empty/>
        </p:input>
   </p:identity>

</p:pipeline>

I would expect this to process correctly outputing a sequence of the 3
root elements  (I also added a p:empty for good measure) ///// its
giving me a XD0007 e.g.

Error  : Pipeline failed: err:XD0007: null  If sequence is not
specified on p:output, or has the value false, then it is a dynamic
error if the step does not produce exactly one document on the
declared port.

is this a bug in calabash or my misunderstanding ?

cheers, Jim Fuller