Commerce View oddities?
The master page is always present in a defined View, although it may not be visible.  To toggle its visibility on and off go to the views list page and select the 'Settings' Tab.  Check or uncheck the "Always show Master Display" checkbox.

When you begin a new view and generate the a page or block, the hidden master is also being completed.  It serves as the template for any new pages or blocks you create without cloning.  I keep the master display visible and will use it as the template for views with many alternate displays.