Installed last night from a clean wipe and I am having this issue. Only thing I have done is sync with my Google account. No other programs were loaded when I started experiencing this issue.
I can respond to incoming messages but I can not create new messages from my contacts. Received texts just shows phone numbers and not the names from my contacts. It seems that my contacts aren't syncing with incoming messages. If I click a sender's phone number it allows me to add contact even though that number is already in my contacts.
After all that, loaded Handcent. I can send new messages from my contacts list but I still see phone numbers, no names from my contacts list.
If you go into google gmail acount and edit each contact... remove all "-" in the numbers... for some reason the new miui will not read numers with dashes in them.
Seems silly to have to go into your contacts on gmail and remove all the '-' from their contact numbers to make a new ROM work. They'll figure it out since it worked fine on their last release.
You can also look at my post in the main thread. I did a Google clean up work around probably not as easy as contact clean up but it worked for me. dancedroid