I don't want to post the whole stylesheet here because it
is rather long and complex, and my only problem is with
this particular template [...]

So what's wrong with posting a minimal, standalone example that produces
the problem, as mandated by the list guidelines? :-) Which are posted to
the list at the beginning of every month and make for excellent bedtime
lecture :-) To quote:

    Illustrating your question with a demonstration of the
    problem. Well-composed questions frequently include a
    small XML sample, an XSLT stylesheet, the results
    received, and the result that was desired - all in
    miniature, to make it comprehensible to readers new to
    your problem. (It is also not uncommon to discover what
    a problem actually is in the process of reducing it to
    an illustrative version.)