Mixmaster projectiles collide with friendly players and you yourself in Lockdown. Also, bullets will sometimes not hit blocks at certain angles, and if they do they only hit 3 times, unlike how the mixmaster bullets used to do when first released.
Also, sometimes the thing does not fire at point blank items.
Correction, the point blank projectile failing only happens in Lockdown, where I assume when you're point blank against something the bullet runs into the player first and disappears. The projectiles from both the standard attack and the charge both do this, for clarification.
Who knows when they're going to fix it. They fixed DA's projectiles some time ago for LD. (had the same bug)
While I can't speak for mixmaster and its collision detection, certain other projectiles have fairly wonky hitboxes against interactable objects; so far I've found that the magnus and antigua's projectiles do this. This also applies to the whole "blank range" bug too.