All messages set to same time on upgrade

Over the weekend we upgraded to Tiger server. Most of the time was dedicated to the awful process of moving mail from our panther server. After trying out a variety of tricks and tweaks posted here and elsewhere all our mail made it-- however, most if not all of our IMAP messages now display in Mail as being received at the same time, 12pm, for each date. In other words, all of the mail received August 20th shows as being received at 12pm. The header info of individual messages seems fine-- when actually viewing the messages the time is correct.

I have tried repairing the database with both server admin and mailbfr, but it doesn't seem to make a difference. I also tried rebuilding the individual mailboxes from the client side. Anyone heard of this and/or have any suggestions? Thanks