A Played ghost is haunting other residentials?

That is a feature. The game doesn't care if the ghost is played or not. A ghost is a ghost. Thus excluded from most sim_filters (especially from service sim roles).

Thus you won't see them out often unless a ghost is required (near their grave, Spooky lot challenge, when a holiday tradition makes ghosts wander in the streets, bar ghost nights, séance tables, haunting maintenance events etc.).
This has been so since ghosts were added to the game 1 month after the game was released and this hasn't changed since then. So yeah, doubt it'll change.

Yeah, like the séance table this would use pre-existing ghosts when possible to keep down townie generation. The séance table will only summon existing ghosts, or generate spectres if there are none.

I don't think it is necessarily a thought-out feature, but I don't think it's a bug. I believe the game is working for you as designed. For the spooky lot trait I imagine the game searches for ghosts in the households (including played ones it seems) and uses them. I think that is better than generating truly random, new ghosts most of the time but I can see why it could be annoying...