Hi Damian,
I am trying to reproduce this, but I don't have enough of your files/setup to do so. The code you pasted there for your component is missing something since it doesn't have a <xbl:template>. Can you create a minimal version of your component and setup that reproduces your problem? (I'd recommend you try it on a verbatim install of Orbeon Forms, so you can be sure that your instructions are complete enough for one of us to reproduce the problem on our side without guesswork.)
Alex
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