This is by design. The Card view only displays scenes that start with a Scene Heading. If you change a Scene Heading to a Shot, it's no longer considered a "master scene" but rather a sub-element of a master scene. If you change the Shot paragraph back to a Scene Heading you'll notice that it reappears in the index card panel (or view) -- along with your scene summary, if you wrote one.
NOTE: The Card functionality in Final Draft 10 is far superior to the one in FD7. Information on upgrading is HERE.
NOTE: All support for Final Draft 7, including software activation, has been discontinued. You may find solutions to problems in the online knowledge base or in the PDF manual found on the installation CD.