My flute recently picked up two hair-thin cracks (one on the barrel and one on the headjoint) that I was going to have repaired tomorrow, but overnight it seems that the crack on the headjoint has disappeared. Anyone ever heard of this happening? It’s a problem since I need to see the crack to have it repaired… and the repair guy is going to think I’m crazy if I point out cracks that don’t exist. I have photographic proof of it’s existence though..
Humidity up or did you oil it? Small cracks can seal back up and be hard to see. Can you feel the cracks at all?
A similar thing happened to me and the crack on my head joint got a lot smaller after humidifying. Denny called it slowly closing the barn doors and that’s what it was like; after a few days of humidifying that crack had shrunk a ton (thanks denny, wherever you are).
Common
The cracks occured during shipment. It’s actually not very humid here so I don’t think that’s what fixed it. I can’t feel the crack that closed up- the flute is bloodwood so there are other gashes and marks that are just the figure of the wood. It was hard enough to see the crack in the first place. I’m assuming I still need to find it and have it repaired? The crack on the barrel isn’t closing up so that’s getting fixed tomorrow.
My guess would be that the flute has a surface check, that will open when the flute is is humidified, and will close when it drys out. (or is it the other way around?) 
The crack is visible again 
although the flute has not been played today and has not left the room it was in. Hmmm.
Quickly mark it with a pencil or some tape then!
Just in case…
A crack is never going to heal itself, it’s just going to appear of disappear depending on the moisture content in the wood. It’ll probably get slowly worse unless it’s repaired.
cracks tend to “disappear” in the summertime (humid) and “reappear” in winter (dry heat)