I have had strains that did that. They would look close to being done and 'BOOM' another bunch of white hairs on the top of the colas. From what I have gathered, and I may be mistaken, is that it is a propensity of some strains to do this. I had an indoor grow, that had never been stressed, of severel varieties that had kept putting on new bud for a full 3 or 4 weeks past the advertised finished time. I just let them go until I thought that they where finished. ( amber/cloudy trichs ). More weight, more bud, not complaining too much.