It's 100% a software issue. This happens only once every two or three days. I know it's a software issue because it will respond to double clicking to bring up fast app switcher. But I am basically stuck in the app I left the phone in because I can't single click back to the home screen. I can usually figure out things like this, but it's got me baffled. Also, respringing will fix it but I want to know what's causing this in the first place.
iPhone 4, jailbroken, 4.0.1
iPhone 4, jailbroken, 4.0.1