I have the EXACT SAME PROBLEM. I also noticed that my yellow tends to have more bubbles too. I came to the conclusion that the lighter the icing, the more the bubbles show up. I've started resting my icing and if I don't have time to rest it, I've been taking a few minutes to tap the bubbles out by banging the bowl on the counter for a few minutes (make sure your bowl isn't breakable!) just before pouring it into my bottles. This has really reduced my number of bubbles, especially in my white flood icing.