from your write up I am assuming you bottle condition with a referment in the bottle.
I use 4 ounces corn sugar per 5 gallons when I bottle.
What did you use? Is there a glitch with your scales?
Those are the obvious questions.
Another question would be all about how much starch you had when you ended your mash.
Did you do a starch test?
If not and you re-fermented ANd pitched a different yeast for the bottling you might have got a yeast that can eat the starches.
Another version of new yeast is that some yeasts don't consume some of the malt based sugars very well and refermenting with a different one can get it going again. So even if you used a proper volume of sugar when you bottled you might have more sugar available that you were not aware of.
I'm out of gas, that's all I can think of.