django-taggit not working when using UUID

I had similar issues, when used GFKs. Adding explicit types cast helped in my case. I'm not 100% sure it will work, but try to do this in console:

psql -d <your_database>
create cast (uuid as varchar) with inout as implicit;
\q

If it will help, you should also do the same for database template1 (which is used as template for new databases creation — it will give you proper setup for the databases created for Django's unittests).