(Excuse the zombie post, but the information is important). It's the maltodextrin. I got surprised last night after dinner at my cousin's house. Couldn't figure out the problem until I remembered the brand of salad dressing and looked up the ingredients. Third ingredient is maltodextrin. I also respond similarly to maltitol. Many people do. Read the hilarious reviews on Amazon of Haribo Sugar-Free Gummy Bears. You have to Google it, because Amazon has pulled the product.
I find it annoying when people who did not have the same experience try to explain that it must be something else. Many reliable sources cite the laxative effect of maltodextrin, maltitol, and sweeteners containing either. I hope that your GI physician has been able to help. I find that Culturelle probiotic helps lessen the frequency, but it cannot counter the powerful agents like maltodextrin, or a load of fat, or a strong allergen (scallions for me; wheat for you). Fortunately, exercise seems to counter or delay the effect of some antagonists, and I have only had a couple of emergencies while cycling. I pack my own food for long rides, and Clif bars for the shorter ones.
Good health to you.