Characters controlling story

Has anyone discovered that sometimes while writing a story the plotline goes off in a completely unexpected way? I know with Bike I have more opportunity to explore cul de sacs than most and then bring it back to the main thoroghfare, but it never fails to amaze me how the story line unfolds in ways I wasn't expecting.

That sounds as if I plan Bike. It should be obvious by now that I don't, I try to follow on from the previous episode or if there's an obvious theme continue it or take it off in another direction. Yeah, there's lots of cliff hangers, but they enable me to change direction or pace. I get grumbles if there's too much action or too much domesticity, so I keep my readers on their toes and they in turn do the same to me.

So, does this happen to anyone else?