I exported my world for a test-play, and sure enough, the spiral staircases are still bugged, and maybe the bug even extends to staircases built in-game :/ I built a house for my test-Sims, with two spiral staircases. Test-sim walked up them no problem, but couldn't get down again. Resetsim didn't work, had to use moveobjects. Then I took her to the pool club, to check there (there's about three sets), and all the mixologists were hanging around in the lobby, pouting because they couldn't get to their bars (they got over it it pretty quickly - they all started dancing in the lobby, see below)
I didn't try deleting and replacing the staircases, although I will next go round.