Ladies and gentlemen, we have a winner!
Many thanks to Faraz for shedding light on this murky area of the Nakisa tooling and to Luke for his prompt and helpful input.
And now for my little rant:
For any Nakisa folks listening, I believe I won't be alone in saying you need to up your game with respect to standards compliance or at the very least providing improved visibility of the supported technical features (e.g. namespaces, XSD or even DTD references would be very useful...).
Otherwise your partners are forced to implement solutions with one hand tied behind their back, which is very frustrating if you're the one facing the customer...
For the rest of you, keep plugging away; one day the light of Faraz may shine on you too 