Shouldn't "AddCustomPhysics" call you back with a WRITE lock

I’m using BodyInstance->AddCustomPhysics to trigger a per-physics update callback to update some physics, but I’m given warnings that at some point I’m trying to upgrade my PhysX lock from READ to WRITE (this is during the callback execution). Surely if I’m applying physics changes then the callback triggered by CustomPhysics should be with a WRITE lock. Or have I misunderstood the purpose of AddCustomPhysics…