I'm now quite sure that this bug is in cairo-dock...
If i replace gdk_window_move_resize() with just gdk_window_resize() (so, like this, dock don't move)
Here what happen then when an icon is closed:
- Dock resize itself
- Icon is remove
- Dock move to it original position !
So, this is the last move that do flickering...
With gtk_window_move_resize(), dock move at an invalid position and then go back to good position.