Yeah, I ran into exactly the same problem when I did the steam effects for the default carrier, Orion.
If the steam effect is given a lifetime, once the effect has expired, it just doesn't trigger again. At least not on the same attachpoint.
On the other hand if you make the effect run continuously, it triggers, stays on until you try triggering it again at which point the effect stops, and immediately does trigger again.
I just don't know enough about the effects engine to know why it works like this. Be nice if someone could explain it though.