Wrong info from your end. It is fact that the login credentials are called upon first opening of the web application (under a fresh start of the browser). As long as the browser window is open after you suceeded to login, PHPRunner keeps that very session alive. If you close the browser, the session ends, thus upon a new login later on, the web application is asking for the login credentials again. Under "security" section within PHPRunner you can find options for the session control, so, if you under a hardcoded (= one user) think it to be very important that you need to pass loging credentials, think about let us say a 5 minutes time of inactivity to be the limit for a session for any user to be set to then end the session inside the browser.
You can visualize it here, you should have tried to reproduce the same before your long reply....