Units have trouble understanding that one must traverse entire length of staircase in order to move to specified location. Many times, units become "stuck" as they try to pass through the railing, as they tend to move in the shortest route possible (AKA: The Straight Line).
Edit: Since the 7/30/2013 dev patch, AI no longer become stuck traversing staircases. Needless to say, the actions are still very "rough", and they tend to fall off staircases at the last 3 steps or so.
Find a metal grate staircase (there are plenty at the docks near the airport on Stratis).
Be on top of the dock, order a unit to move to the lower section of the dock (at sea level). Be sure this location is not going to result in a "straight line" path down the staircase. I would suggest placing a ship or sub near perpendicular to the staircase, and order the unit to board.
With this unique set of commands, please note how the path selection will make the unit choose to "hop" from the staircase (as it is a no-harm fall), and become stuck as a result.
Mass closing ancient tickets with no activity for > 12 months; assume fixed or too trivial.
If this issue is still relevant in current dev build, please re-post.