Day 030/19. This is weird.

I know I did a raindrop a couple of days ago.....but how about this?
I went out with my macro lens today to catch the frost. But what intrigued me most was spotting this drop caught in the buds on one of our bushes.
Look closely and you can see that it is a perfectly formed frozen drop, but with air bubbles suspended in the ice.
So how does that happen? My only thought is that it partly melted and then refroze. I never noticed this before, so perhaps its rare...or perhaps I've only just noticed.