Appears to be the rain droplets.
It should be noted that I had to create a new world in order to play again.
2013-01-31, 11:12:45 PM UTC
Rain will fall through upside-down stairs when they are placed with no blocks above them. Screenshots aren't as good as I was hoping, but I think the gist of the issue is there. Small graphical bug otherwise.
Chris
MC-8858
Appears to be the rain droplets.
It should be noted that I had to create a new world in order to play again.