Interesting. Thanks for the post and blog. I think the Dave Watson reply nailed the reason for the over carb. Dave said, "Thats pretty cool! My guess would be that you had a wild yeast in there that took it down to 1.010 quickly, but some other buggies kept on working, albeit at a much, much slower speed
".
I am in the process of isolating wild yeast from strawberries. However, instead of just fermenting with whatever grows in the culture, I am isolating pure cultures from the initial culture. What I got was 2 different yeasts. One grows fast on a plate (similar to Saccharomyces) the other very slow (similar to Brettanomyces). Still in the process of trying to determine exactly what they are but my guess is Sacc and Brett. You may have caught a similar culture and the Brett continued to chew through the unfermentables and your priming sugar. Perhaps next time you could try giving it a couple of months in a secondary.