I don't know why this is happening, when I outline my cookies with RI once they get semi dry they either bubble or crack in the corners. Anyone know why. I colored my icing last night then outlined this morning.
I'm not sure why your outlining would bubble, but the cracking could happen if your RI is too dry. I'm not sure if this helps, but I'll give you a little bumpity-bump Maybe someone else has an answer. Good luck!
Mine would sometimes crack also and I did find that if I went over that area with a moist paint brush it would smooth it out. That is when I fingured out that it was probably too dry and added a little water and it was much better. Hope that helps!
Can't help you out about the bubbling though, sorry!