Report Builder connects as who?

I am running SQL 2012 with SSRS in Native Mode.  If I am logged into Windows as one user, but I am running Report Manager as another user.  When I click the Report Builder button, it automatically connects to the server.  Once in Report Builder, I was able to open and overwrite a report to which the user that launched report builder did not have access.

This leads me to believe that even the ClickOnce version of Report Builder inherits the connection information and permissions from Windows and not from Report Manager.  Is this the intended functionality?

Ann Weber