OK, here are my thoughts:
MC is incorrectly described in the medical journals, as a disease of the colon, (only). We, (the members of this board), know for a fact that it can affect any part of the digestive system, from mouth to anus, similar to Crohn's disease. Collagenous gastritis, (thickened collagen bands in the lamina propria of the stomach), and collagenous sprue, (thickened collagen bands in the lamina propria of the small intestine), are 2 examples of MC symptoms in the stomach and small intestine, respectively. In addition to that, examination of biopsy samples from the stomach and small intestine of patients with MC will frequently show lymphocytic infiltration, (the primary marker of LC), in the mucosa of the stomach and the small intestine. If it quacks like a duck, . . .
Interestingly, lymphocytic infiltration of various areas of the small intestine is virtually always present with celiac disease, also, which certainly suggests a common link between the two diseases.
But I can't answer your questions about "instant" bloating.
The gas that produces bloating is generally a byproduct of fermentation by bacteria, and fermentation is a time-dependent process - it doesn't happen instantly, though, of course, it can be initiated almost instantly, and from there it propagates somewhat rapidly. The colon is notorious for fermenting carbohydrates that arrive undigested, (or partially digested), and this is the mechanism by which it "digests" food that reaches it in anything less than totally digested form. Also, due to the time-dependent nature of water extraction, passage through the colon allows sufficient time for a substantial amount of fermentation to take place, if the feedstock, (undigested food), is available.
Transit times through the stomach and small intestine are typically much shorter, and ideally, bacteria with a penchant to promote fermentation should be absent in those segments of the GI tract. With MC, those transit times are even shorter, so that reduces the odds of fermentation even further, as a possible candidate for the cause of rapid bloating.
SIBO, (small intestinal bacterial overgrowth), where bacteria normally found only in the colon, somehow manage to migrate into, and establish colonies in the small intestine, might explain rapid bloating, but even then, it would seem logical that a certain minimal amount of time would have to pass before enough gas were generated to create a bloated condition.
So what does this leave as a possible suspect? I'm beginning to suspect gastroparesis. Gastroparisis, of course, is incomplete, or delayed emptying of the stomach contents, due to compromised motility, caused by a failure of the normal peristaltic pumping action of the stomach muscles. Bloating is a common symptom of gastroparesis, because is allows undigested, (or partially-digested food), to remain in the stomach too long. Usually, though, gastroparesis is accompanied with a feeling of premature fullness, (after only a few bites of food are taken), and nausea/vomiting is common/typical. I often had major problems with gastroparesis during the early stages of my reactions.
Accute gastroparesis is usually pretty obvious, as it can sometimes present virtually as a blockage at the pyloric sphincter, (the "valve" between the stomach and the small intestine), but I can see how a limited degree of gastroparesis might result in a failure of the stomach to completely empty, thus setting up the opportunity for fermentation, since the means of starting the fermentation process would always be present, (in the form of rotting food, that shouldn't be there). That would appear to present a scenario whereby almost instantaneous fermentation could result, (IOW, as soon as "new" food entered the stomach, the existing small supply of decaying food could quickly propagate fermentation of the added foodstock, before it could be properly converted to chyme, by the normal digestive process.
Another possibility that comes to mind would be inadequate stomach acidity. If the acidity of the stomach is not adequate, (IOW, if the pH of the stomach is not low enough), digestion cannot initiate properly, and food will spoil very quickly in that warm, moist environment - plus the fact that a pH that is not low enough will allow any bacteria that might be present to not only survive, but thrive, (and thereby initiate spoilage very quickly). The pH of the stomach should be in the range of 2 to 3, for proper digestion, (7 is neutral, and anything above that is alkaline, of course).
Other than by swallowing several whole Alka-Seltzer tablets, I don't see a logical mechanism by which "instant" bloating could take place, unless some means were always present for initiating a fermentation process in the stomach, and/or duodenum.
Patc,
FWIW, iceberg lettuce is so irritating to the colon, that it virtually guarantees a reaction for almost anyone with MC. It was so bad for me, that even though I've been in remission for over 7 years now, and I could eat lettuce now if I wanted to, I have never had a desire to add it back into my diet. Even so, lettuce shouldn't cause instantaneous bloating, unless it directly irritates the lining of the stomach; and, of course, that suggests gastritis.
Tex
Visit the Microscopic Colitis Foundation Website
I'm not a diabetic, but it's possible that I may be an celiac, FWIW.
My first thought was, "Wow! This is cool - no more nostril-searing odors to have to deal with at Potty time". 
Unfortunately, once my gut began to collect the normal populations of gut bacteria again, my "sweet-as-a-baby's-breath" fragrance, slowly disappeared. 
It took over 2 months for any noticeable changes to initiate, but once it began, things went downhill in a hurry, and after a couple more months, the "bouquet" was pretty much back to normal. 