Activity API don't update

When you pass in an id with the params (by the way, is it supposed to be 'id' or 'activity_id'? Either way it doesn't work right now) and call 'activity', 'create' (or 'activity', 'update') instead of updating the activity, you just get an error message saying: "DB Error: already exists"
Well of course it already exists, that's why I passed in an id and some updated params!
Unfortunately, arguing with the API error message fails to convince it to behave differently