Shabbos 42 – שבת מב

We learn that according to Beis Shamai cold water is not to be poured onto hot water contained in either a Kli Rishon or Kli Sheini.  Tosfos explains this is due to a concern that one may confuse the Kli Sheini with a Kli Rishon. In the following Mishna we learn that seasoning may be added to a Kli Sheini but not a Kli Rishon, and this seems agreed upon by all.  Why is there no gezeira here according to Beis Shamai