I have also found a set of stairs which cannot be climbed while in any crouched position (low, standard or high). It is in Agia Marina on the side of the building at the editor XYZ position (2987, 6066, 7). I have uploaded a picture of the building. I can always reproduce this.
May 9 2016
Sorry, I uploaded a file to the issue in the wrong tab.
While shooting from the fast pace, the character should switch to the slow pace until he stops shooting, and then resume the fast pace.
I have even heard a gunshot as if I was standing next to the shooter while flying low in the helicopters showcase mission.