For example - place a permanent skill remover half way up a wall, and assign a climber to climb up it. The lemming will encounter it, lose his climber skill, but continue climbing this wall (when he falls off it, he won't be able to climb the next one).
Similar cases apply to all other skills (except Disarmer which this situation can't really occur for).
This was a (major) oversight, rather than "I implemented it but it isn't working properly".