I think it might have something to do with the surrounding scenery.
I tried it out of Friday Harbor Brian which doesn't come any more default. I remember the smoke coming and going while it was in beta for little or no reason. That said, I had a look through some of the old betas this evening and some had smoke entries in the cfg and others didn't. This in itself is an obvious reason for smoke appearing then disappearing but adding the smoke entries hasn't brought it back I'm afraid Never mind