I'm having the same issue. I've upgraded to 4.1 and every time I try to send a text, as soon as I start to type, it flips back to the home screen. I've shut it down several times. Same thing. Any suggestions? Very aggravating.
I've restored it and it's still happening. Not all of the time, but most of the time when I tap the text bubble, it will open and then flip back to the home screen. It's such a nuisance. I guess it's time to call apple.