Why it happens
Pastry shrinks because of gluten, the stretchy network that forms when flour is mixed with water and handled. Overworking the dough develops more gluten, and stretching it to fit the tin pulls that gluten tight, so it springs back in the heat of the oven. Pastry that hasn't been rested and chilled hasn't had time for the gluten to relax. Blind baking without baking beans or paper lets the sides slump too.