This is very easy to replicate and seems to be a huge oversight. I expect it should be fixed very soon. Start playing music through the speaker on your 900 using the music hub and then press the windows key. The tell me client will pop up and the capacitive keys will become non responsive. Turn the screen off and back on,slide up the lock screen and press the back button. Every time you press it for a short time, not a hold, it will bring up the multitasking cards. On my phone this also killed the camera button from waking the phone, but that may be coincidence. All I know is I cannot play music on the phone and navigate, and my camera button does not wake up the phone.