Hi,
I have done an upgrade from Alf 1.4 community (I chucked a fair amount of stuff in it inc extra users, groups and categories) to 2.0 community and did not encounter this issue.
As Kevinr mentioned, did you clean out your Temp, Work and webapps\alfresco folders to eliminate any old 1.4 files?
If you have any further information about your set-up and how you reproduced this bug that would be useful.
Thanks,
Steve