This most often has happened to me when climbing to the second or higher floor of fire stations. It has also happened when walking around the second floor of some regular houses, as well as on the rooftops of hospitals and police stations. I have absolutely confirmed that this is a real, genuine bug, because it has happened a number of times when no one is around, and it always results in my character's shoes and pants, along with everything else in the pants, to be ruined, while all the other items take no damage.