I had the same problem and what I did was delete contacts reboot then restore from backup with only "communication and Calendar" selected.. Now all is good.

EDIT: sorry should have been clearer .. My problem was with only one contact also.. i delete that contact and did the steps above.

yes they are. I only have the issue with the one contact. Ill try what blackopz suggested and post back.

if u click on that one contact after u send something, if u scroll up dont u see previous messages?

No the messages still show. Its when i close the window and open it again that they all go away. Deleting the contacts and restoring them through ovi suite fixed it for me.

hmm.. had the same problem. Don't know what happened. i had installed chrome before this problem occured on the overclocked device. phone had crashed too when i was in a call and with some browser windows opened. Not only the messages not getting stored, the call log was empty all the time. I deleted the contacts, did a reboot and restored Conversations and calendar from a recent backup. That worked for me.

In case anyone else is wondering, you can access the complete file system using ssh, including the conversations database.

I do not know about any problems people are having with contacts, but I finally found a fix for the various problems I was having with Conversations.

See my post here for details