I feel like it did strings in postgres too, not too long ago and I had a <brain explode> moment when I worked on a codebase and had to figure out why queries were terrible
Actually now that I remember we were using MySQL and I was pushing for migrating to postgres partially for this reason, sorry it was a long time ago in startup time
https://docs.djangoproject.com/en/1.8/ref/models/fields/#uui...
It may not have worked correctly on your project for some reason?