This seems to be a bug and it happens not only for medium sized wings.
What I think is going on:
the game has to decide somehow if a wing is a "front wing" or a "tail wing", because depending on the position of the wing, the direction of the control surfaces has to be inverted.
For example if you want to pitch "nose up" (pressing S), a tailwing's controlsurface has to be angled up while a control surface at the front of the aircraft has to be angled down.
I've put together a minimal aircraft to troubleshoot the issue and I was able to reproduce it by moving the wings or changing the "wing angle" in the proccedural wing configuration.
I'm not sure which information the game uses to determine whether a wing is at the front or the tail, but I guess the position of the wing's "center of lift" gets compared with the aircraft's "center point" (maybe the center of mass?!).
