Ubuntu 14.04, Gnome 3 fallback, nvidia graphics
Blender 2.78c, Blender 2.78.5 2771f602e6
The way camera object is drawn in the viewport switch behaviour with orthographic camera, compared to perspective and panoramic cameras:
Changing the focal length squishes the camera object, but orthographic camera changes size. Changing the display size on perspective and panoramic cameras changes the size as expected, but orthographic camera squishes. The problem being that one can't change the orthographic camera display size and not have it block the view without changing the zoom level. Could move it out of the way, but then that could start messing with set clipping settings.
This behaviour doesn't seem intentional so posting this for you to check
Exact steps for others to reproduce the error