Is it my imagination or are followers seemingly reluctant to use stairs when I leave them in a location? Lydia, for example, always seems to stay upstairs in Breezehome, and all my followers I've left upstairs in the main entrance chamber of Fort Dawnguard never go down the winding stairway to sandbox around the fort.

It's because Lydia stumbles like a fawn when walking downstairs.

Never actually noticed that.