This is getting off-topic for this thread, but I don't think there's been a correct fix posted for this. I've hacked the import script to do this (among other things, which I'm still working on), and it involves numerous changes.
Donate to UBBDev today to help aid in Operational, Server and Script Maintenance, and Development costs.
Please also see our parent organization VNC Web Services if you're in the need of a new UBB.threads Install or Upgrade, Site/Server Migrations, or Security and Coding Services.