In regards to the post right above here...your situation is a little different. You aren't "quitting" your MPH per se. You are staying in until such time as you get a med school admission.
Not sure how this will look to adcoms, but I wouldn't worry about it too much until you get to the interview stage. With your MCAT scores "expiring" I think you have a good reason to try now. I think it's OK to be honest with the adcoms about your reasons for doing this, and explain to them that though your desire to get your MD is paramount, you'd still like to finish your MPH. The die is cast now...you can't help it if they hold it against you. Some adcom members may, but I think some won't either. I would personally look on this differently than someone who had just quit an MPH program. Just be ready to explain during your interview what you have learned from your MPH, and if you have a plan to finish it (i.e. could you transfer your MPH credits to this new medical school, and/or take online classes to finish, or maybe keep working on your MPH the summer between 1st and 2nd year of med school, or maybe finish it after 4th year of med school?). Before you go on each interview, do research on the med schools where you get interviews...check to see if they offer an MPH and if so, try to see if they accept transfer students. Then you can show the adcom that you have done your homework and have a plan. If they don't offer an MPH, it will be harder for you to explain what you plan to do, but you can always tell them you plan on finishing it during residency. Also, there are some mostly online MPH programs (U of North Caroline, for one). I guess you could say you're planning to finish it that way...but be realistic and realize you won't have time for that during years 1-3 of med school, most likely.