Confusing search interface and search results

It seems impossible to search for coins selecting a specific Compostion

the only filter available in Search interface is called Composition 

but it's in reality Material

or Core or Plating

when looking for Gold coins I would like to find Single material gold coins only or Gold plated coins only, not both

https://en.numista.com/catalogue/index.php?r=&st=147-150-149&cat=y&im1=&im2=&ru=&ie=&ca=3&no=&v=&cu=&a=&dg=&i=&b=&m=6&f=&t=&t2=&w=24-24&mt=&u=&g=&c=&wi=&sw=

Related https://en.numista.com/forum/topic161074.html