Bottled this yesterday and poured myself a wee glass of flat beer. Seriously tasty stuff - like a citrusy Orval (with Cascade and Nelson hops). Definitely Brett going on in there, fruity funkiness mixes well with the hops and grape juice, and there is a slight sourness that is difficult to tell apart from the hoppy bitterness. Tastes like the best white wine I never had. Saved a gallon in a glass demijohn (I ran out of bottles), might toss some oak in there and see how it goes.
As to where the brett came from all I can think of is that I made a mango ipa with orval dregs 6 months ago. The only piece of equipment in common was the siphon wand which i left in one of my ferementing buckets. I can only assume i didn't wash either of them thoroughly enough and the brett from the siphon wand has been chewing it's way through some sugar in the bucket. And i'm quite happy it did