Confusion on how Category List Page works with filters

I was going though the demo site and looking at this page.  

http://demo.smartsto...m=1&ram=opt4794

Now you can see on that page I am filtering the Arbeitsspeicher to 8 GB.  

Now when you go into the product I can see there is actually 2 options on the Arbeitsspeicher attribute for that product, 8 GB & 16 GB.  Why doesn't the 16 GB show up as an option on the Category List page?