I can confirm this. Toxic is supposed to always hit when used by Poison-type Pokemon, even if the target is in an invulnerable stage due to using a two-turn attack.
This bug affects pure Poison-types, primary Poison-types, and secondary Poison-types. I've tested with Salazzle, Toxtricity, and Muk against a Pokemon that spams Minimize, a Pokemon that spams Fly, and a Pokemon that spams neither. I was always able to get a miss. This happens on both the user's side and the opponent's side, and regardless of whether the Poison-type Pokemon moved first or last.