I have a robot, when parenting one object (upper arm) with a specific bone, ctrl_P and selecting Bone, causes the object changes its position. I have no idea why. Can someone give me a clue? with the lower arm, there's no problem at all. I'm using Blender 2.69.
It was my mistake, the object was previously parented with another object, so, when re-parented the object with the bone, its position is now referenced with the position of the bone, forgetting the previous spatial reference with early parent object, so it cause re-positioning :-)