Why Do Pluto and Charon Share the Same Diffraction Spike Orientation?

[Imager]

Below is a shot of Pluto and Charon from Hubble in 2006. I was wondering why the vertical and horizontal planes appear brighter in the same direction for both objects?
I thought the increased "twinkle" at perpendicular angles was normal effect from objects and didn't have any particular orientation. That made me think it was odd both these objects had the same orientation to their brighter “twinkle”. Is it something to do with the optics of a telescope?

Also, is there actual name for this effect, other than twinkle?

Link:http://hubblesite.org/newscenter/archive/releases/solar-system/pluto/2006/29/

 

[mfb]

This is not an effect of the atmosphere. Those lines are from the telescope (from the support structure of the secondary mirror), and the telescope is the same for both objects: Diffraction spike.