What should happen is that the first time you use the App, you go are sent to the login page, you enter the IP etc. details and tap "OK".
This sends you to the screen with the buttons. You should only be sent back to the login page if you tap the "LOGIN" button at the top.
Even if the details are wrong.
If you checked the "remember details" box you will not be asked for the IP address etc. again, and will go straight to the button screen.
You should use the credentials that work with the browser. As you speculated, the App does indeed try to simulate a browser.