Okay, so I know there are several theories as to the cause, but can they be repaired???

If anybody has any suggestions, I'd be very appreciative!

Are you talking about a bulge from the layer/filling area?
If so, when leveling your cake check the sides.
Once I started trimming them back, my blowouts stopped.
Thanks, SugarShack!

To me a blowout is where the icing pushes away from the cake. I use a toothpick and poke a small hole to let the air out and then push it back to the cake.

Sorry, I didn't get notification that there were replies to my post. Thanks for taking the time to help me.

It's the icing bubble, not a filling bulge (yes THANK YOU Sharon )!

I smoothed it back as best I could, but didn't poke it - I sure hope it doesn't come back.

I've only had that happen once before. I let my cakes settle, don't know what happened. I am a nervous wreck that it will happen on a wedding cake next weekend. FINALLY got the smooth icing down, use SPS for worry-free transporting, and now THIS...

i have also had this happen especially when pushing in plastic dowels or posts for sps, slow and steady and do it early. i think the compression created by the pushing makes a bubble that needs to escape. sometimes they don't show up until later (well after being inserted), so i do everything well in advance, so i can repair them in the conveinece of "my" kitchen with all my supplies.