I've had that problem too a couple of times, where I've had a message and it's just disappeared when I tried to read it.
Actually, I wonder if anyone knows anything about the predictive text bar (the bit where it gives you options as to the words you might be typing) moving so that it covers the bottom row of letters? It's so annoying because I can't type most of the words without choosing the first part of the word first to get rid of it, and then finishing it off. Taking 3 times as long to do anything.
I do like Handcent but I'm thinking I might switch back to the default Hero service because these issues are getting a bit frustrating.