(My phone is myTouch 4G running Froyo)
I have been testing some simple apps and when I "Quit" the app it closes, but in Settings...Manage Applications, it shows it as still running under the Running tab. If I try to repeatedly launch-quit-launch-quit..., buttons start dissappearing, the app quits working, "Quit" quits working, then a force close will bring things back to normal again.