Missing task items after Import-SPWeb

Hi

I've backed up a site using powershell and then restored. One list workd fine but the Task list is created but does not show any items.

The task list has items that have been created with unique permissions, however I have added myself to one of the items and tried to import but even this gives a blank task list.

What could be wrong?

Export-SPWeb http://mysite -Path C:\backup.bak

Thanks