I think we can eliminate the weather as suspect, what you described is exactly my z6 weather and no bud drop here, in fact I expected some drop with the huge amount of them set. Allot of plants abort some of the buds if not happy. In my experience with other plants it is usually not enough water, or some other kind of stress.

My plant does have alot of buds on it as well as there was one very hot day that it got wilted a bit but revived very fast with water. I was watering 2 times a day in the hot weather but now that it is cooler have gone back to once a day. Even with the bud loss I expect quite a show the blooms are just spinning open I will try to post a picture in it's glory. I am looking forward to adding to my collection of brugs as cuttings become avalible.