Dona and Econlady, I have never used vinegar before, and always thought it was just to remove grease or oil from tools and bowls. Apparently plastic bowls have a porosity to the surface that makes them more likely to harbor residue. I have never before seen someone who had icing breaking and fixed it with cleaner/vinegared bowls. It is definitely something interesting to try out. Do you rinse it with water after, or just let dry?
Dona! It sounds like royal icing is afraid to misbehave for you too. �� You said they all came out fine, but was there any difference in the appearence when they dried? Was the icing any more shiny? How much corn syrup did you add?
Congrats on piping your lettering! I knew you could do it, and I will be waiting to see if you post photos. I bet you get better all the time.