reference data disappearing after pytest run?

[ccurvey]

I'm sure this is something I've done; I'm hoping the community can help me figure out where I went wrong.

I'm using pytest with Django. In my migrations, I create a Category class, and populate it with reference data. I have --reuse-db in my pytest.ini.

A few days ago, some of my tests started failing because some of my Category reference data was missing. I can get my tests to pass if I specify --create-db on the command line. However, after a test run, the Category table exists in Postgres, but it's empty.

Anyone seen something like this before? Any ideas on how I might be able to track down the issue?