Pressing 'Tab' will move certain bones slightly I know that pressing Tab does not change the position of the skeleton in edit mode and pose mode.

When I press Tab, the skeleton of hand are moves a little strangely.Other bones do not move.

What causes this problem? 

Here's a video that shows the problem: https://youtu.be/BGQlwQkXdns

Here's the .blend file: https://www.dropbox.com/s/ji4xjti2umhoxcd/2b_08_middle%20of%20additory%20bones.blend?dl=0
You have a IK-solver applied on some bones. This constrain does not work in edit mode, so when you go to object/pose mode, constrain starts to affect and moves bones a little. 

Other thing that you show in video - it is bone in the head, it is hidden in edit mode, so you need to press Alt+H to show it.

And by the way, do you know that rigify addon, that you use, has a Rig generator, witch builds all logic for you and you need not to add constraints and additional bones manually?