I have this problem with my Thunderbolt. It only occurs when I address the message by replying to a prior message. It has never happened when I choose a contact from the address list. Anyway, I caught it several times so I started to watch carefully that I had the right contact before tapping "send". That didn't help. The personal message would go out and the screen only then showed the message context was not in an entirely different contact's thread - usually a work contact. What a disaster.
I have this issue on all roms not based off of the 2.2.2 except miui ...ota update pushed by vzw. The issue was fixed for the og droid in the ota. The rom I'm on now is the only one that doesn't have the issue ... for me at least.
I'm on metickones stock rooted 2.2.2 ... I still test miui and have never had txt issues using miui.