I found a problem in the latest ROM. Camera app doesnt react on touch inputs when starting it. I experience it in every former MIUI release and it is still there in your 2.7.3
yes i have been using previous camera.apk for this rom due to the recent versions camera.apk have been crashing on video recorder. some features will not work on the camera as you stated. sorry for this i am not sure if it is a nexus s bug or a problem with the app and the rom.