I've been playing the flute for 3 years going on 4 and I've never really needed to practice. At first I had a hard time getting one note out but from then on I didn't have the need to practice. I've noticed that even though I don't practice, I get better at the songs that we play if I know the correct rhythm. Last year I remained in the first chair flute for the whole year without even practicing out of class. I was one of the best in the band and tried learning the piccolo (even though middle school bands don't have piccolos).
I play in a high school band which doesn't allow me time to really focus on the things I need help on. Sometimes we would get music to play and I would need to practice it but never do. The next day, I would be able to play that part even though I never worked on it. It would only happen if I knew the correct rhythm. My teacher can usually tell if a person practiced before and he commented that he thought I had when I didn't.
Also I take flute lessons and I have made huge progress. I never practice the songs that she gives me, and I don't even take my flute out of its case unless I'm at school. I get better at it even though I don't practice.
Also if I concentrated too hard on trying to get the correct rhythm then I would mess up a lot. If I didn't concentrate as hard or hardly then the notes and rhythm would come more naturally to me.
Also when sight-reading songs for the first time (playing songs that we don't know and read it) I could guess what would come next and it would be correct. I would be reading the line about it then come to the end of the line and would know what note and how long to play it would come on the next line. Am I just reading the music and can guess at what would come next or am I seeing what will come next unconsciously?