iPhone Screen Gets stuck in Phone Application. ideas 3G

Ive restored my phone and still running into this problem. When I am in certain applications such as text, calender, email etc.. I will press down the home button and it wont return to the home screen. After pressing the home button again, but it will jump to the phone screen instead. Its as if it thought it was at the home screen originally except at this point I can press the home screen over and over and it will not leave the phone screen. The only way to return the phone to normal is to do a soft reset. This is happening about 2 to 3 times a day. Is anyone having this issue and if so is it software related or is this something I need to go get checked out by the genius?
Macbook Pro Mac OS X (10.5.5)