Go with your original thought on it I'd say . .flush it and leave it a while longer. I have seen other peoples grows (hey you know what dudes are like - cant help but show off. !!!) where this has happened. . plants look as though they r nearly ready and all of a sudden they go again - I've heard it referred to as " Podding " - then they start to brown off and woosh they can go a third time.!!! . . .but maybe that guy was right about it being heat stress ??