I can't exactly pinpoint when this started happening but it's definitely since 2.2. It could also be a strange launcher pro or Goto issue as well. Previously when I would be in an app say handcent and hit the back button, it would eventually bring me back to my home screen. Now when I do it it will bring up my lockscreen (using Goto) and I will have to unlock the phone again. It happens with a variety of different apps too. The strange thing is if I reboot the phone it will function normally for a while and then it will start doing it again. Anyone run into this?