Another thing I've heard about but not seen is when you tension the spokes you should actually go slightly past the tension point then back it off very slightly. This is to "untwist" the spoke. I've heard if it's not done when ridden the spoke can unwind and then be loose. If your builder didn't do this maybe that's whats happening. That said I haven't done it on my builds as I find a good de-tension does the same thing but everyone builds differently so who knows?