The best answer I can give is...yes. ::grin::
My characters come to me fully formed, with their pasts, presents, and futures already filled out. I'm basically a stenographer - for lack of a better word. I write down the things they tell me, and try to make it all sound writerly and artistic.
That doesn't mean I know everything, though. Sometimes, I interpret the characters' stories incorrectly. I make assumptions about who does what and when and where, and I'm always surprised when a character cocks an eyebrow at me and asks how I could've mucked it up so completely.
Not to mention the rewrites. One story I recently submitted went through four different openings, and several different settings before I finally understood what my characters were trying to tell me.
Sometimes, I get the timelines wrong. I forget that the characters as I meet them now aren't necessarily the same as they were when they went through what they're telling me about. For instance in one of my upcoming Breathless Press releases, one of the main characters has a different job in the story than he does as I know him. By the time I've met him, several years have passed since he began living with his lover.
So, do I plot and plan, or do I wing it? Yep!