[Staging] Can't be admin AND member when one create a new Circle

Using Django admin, if I create a new Circle and set the same user as the owner and as a member, I get a 500.

[busyness] 5s average busyness is at 100%, will spawn 1 new worker(s)
spawned uWSGI worker 2 (pid: 1788116, cores: 1)
spawned 1 offload threads for uWSGI worker 2
WSGI app 0 (mountpoint='') ready in 0 seconds on interpreter 0x1487720 pid: 1788116 (default app)

Using the front-end, I'm able to add duplicates of the same user to the circle without a 500, jeopardising the integrity of the database