mysterious crack in door panel

[pmx_super]

Last night a crack appeared in one of the panels in a 6-panel door in my house. It's a small square panel at the top of the door, and the crack runs from the top to the bottom and is through the whole depth of the door.

Any ideas what could have caused it? I'm thinking it might have something to do with the temperature differential between the room and the hall...

 

[gorgeousgordy]

You've probably had your central heating on full blast for the last couple of months, I know I have, and the door has dried out.

 

[big-all]

panels should be loose fixed with only one dot on top and bottom to stop ratteling
if the panels have been painted or glued in they can crack as they shrink