This is so wonderful...to have a place to share and discuss issues with experienced decorators (or novices like me who fly by the seat of their pants and manage to come up with some experiences - good or bad). Have to say thank you Julia for making this happen!
I tend to agree with the surface tension theory. I used the same icing on a couple of cookies and only the "coconuts on the palm trees" had any issues with craters...and they were really deep holes (they were not air bubbles I don't think). I believe the outside crusted rapidly where the fan hit the sides and the center-most spot caved. We decided to call them eyes in the coconuts...and I even had people ask how I had made that detail. I just chuckled. I need a dehydrator badly!