Well I will say that I had never experienced the issue at all. 5 taps, about 9 months old, each had a few different beers in them. Each tap had a quick star San flush immediately before being tapped. Then only last leg change, I did a star San flush, but the beer wasn't tapped right away as I had to do something else for a few hours. So it soaked during that time. When I tapped it, I got hit with a sulfur blast. Now I haven't smelled any through that tap again, but clearly the acid hit did something to the tap. If it had soaked longer, it may have caused the permanent odor that is described above. I am not going to push it but it sounds to me like the acid soak triggers the problem, probably by exposing the sulfur in the parts.
Commercial tap houses probably don't experience the issue because they don't clean their taps!!