Warning on dried mushrooms

Whoever does the cooking of mushrooms please note this warning on sulfide residues in dried mushrooms.: I was in China recently and we went to a few "mushrooms steamboat" restaurants where we can select all different kinds of mushrooms to put into our steamboat. It was very good.The waiters in ALL such restaurants told us NOT to eat until the soup has been boiling for at least 12 to 15 min.In the