I'm seeing the same thing with MIUI as well, both the Lite and the Full versions of Whitenoise. Wasn't happening on Cyanogen 7.2 or Pyro. (actually the Lite version is pure white without the edges showing, but same sort of behaviour -- no UI and Menu button doesn't do anything, have to kill the task to get rid of Whitenoise running)
I am uncertain as to what can be happening here that causes a conflict with the MIUI roms because we are not doing anything special in terms of the interface, buttons, etc. It is near impossible to test on all combinations of devices, android versions, and custom roms. I will take a look for anything obvious, but cannot guarantee anything.
I apologize for the delay as I have been on vacation for the past week, so I have not had a chance to look too far into it yet. I will be loading MIUI on one of my devices as soon as time permits and will go from there.