I had this issue for over a year, and even had an open ticket with HTC about it, wit no success in curing the problem.
What's happening is Sense is crashing. I've posted this issue on other DInc2 boards; it's not a common problem, but others have had it. i thought it might be related to specific apps, but after much experimentation I could not find out what was causing it.
It would seem to happen sporadically - it would occur almost every time I return to Home for a week or two, and then mysteriously stop. Then it would reoccur a few weeks later. I love the phone, but this was maddening.
What I finally did - I stopped using Sense. I loaded Go Launcher, and I use that for my Home screens.