Your complaint is fairly unusual. There is no specific known condition where someone sneezes because of something "extra sweet." That being said, there are some potential causes of your symptom. If this is bothersome or severe, I would recommend that you discuss this with your primary care doctor
Fundamentally, a sneeze is the way for the lining of the nose and mouth (known a the nasopharyngeal mucousa) to clear itself from inflammation. There are many causes of inflammation. Infection is one, which is why people sneeze from a cold. A second cause of inflammation is allergies. An allergic reaction is a common cause of sneezing. Direct irritants are also causes of inflammation.
So the question is why is there inflammation in your nose after eating something sweet. One possibility is that you are allergic to some component of the icing. Many dyes and perservatives in processed foods can cause allergic symptoms. The second possibility is that one of the dyes is a direct irritant to your nasophaygneal mucousa.
Another possibility is that this is not a direct relation. I would recommend that you test this theory a few more times with the icing. It would be less likely for this relationship to be true, but not impossible.
Talk to your doctor if you have more questions.