I had several problems with my state of residency this past application season, so you have my sympathy. Let me echo was Dr. Midlife said: it is absolutely possible to be without a state of residency for medical school admissions and tuition purposes. I saw it happen to a friend, and I only narrowly avoiding it myself. Keep in mind that federal classifications of residency do not overrule each med school's own rules for state residency. The biggest things that I didn't know prior to applying is in states with multiple state schools, each state school can have a different state residency policy. One school may give no challenge to proving residency while the other will challenge you. Absolutely do what the above poster suggested and call EACH school you're interested in applying to in order to get the full information. Unfortunately, some schools still won't give you a straight answer... but it's better than nothing. Another thing to know is that some schools set deadlines as to when you can declare/switch state residency.
I started out declaring my home state as my state of residency only to be rejected. I had to switch my residency status (thankfully very early) during the application season.This caused me to be challenged at one state school, which I won by providing income taxes, a letter of employment, and confirmation of my address. The other state school did not consider me as a state resident despite the other state school doing so. It's a jumbled mess at times. Good luck, and definitely get this sorted out before you apply. You'll regret it if you don't.