One thing I noticed about the DB challenge were the numerous "DO NOT OVERMIX/BEAT/BLEND. Wise words to be sure, but I noticed a number of people having problems with the buttercream.

You probably underbeat.

I did an experiment a few months ago because I had some extra cream and thought it would be fun to make butter with the kids. I wanted to see how long it took to overwhip the cream. I whipped for about 15 minutes before I got butter. The cream stayed in a usable consistency for about 8 minutes. This is good to know, as before I was so scared of overwhipping my cream that I usually had more of a puddle than a dollop.

I have never beaten eggwhites so long that they collapse, but it seems a worthwhile experiment. Next time I make hollandaise, I may do just that. Then I'll have a handle on how long soft peaks are soft, stiff peaks are stiff and when destruction is eminent

Anyway, you cooks out there might want to try the same thing just to watch the changes that occur. You may find it takes longer to overbeat than you thought.

And your buttercream might be more successful.