Adding a constraint to a base trait breaks a derived trait?!

I've been using Rust for years and I've encountered a new problem that sure feels like an unnecessary language limitation, where adding a constraint to a trait breaks another trait that's derived from it, for example:

trait AddToI32
where
    Self: Sized,
    Self: Add<i32, Output = Self>,
    i32: Add<Self, Output = Self>,  // this line causes an error
{}

trait Subtrait
where
    Self: AddToI32,
    i32: Add<Self, Output = Self>, // this line makes the error go away
{}

My thinking is that the offending trait bound in AddToI32 should result in the bound i32: Add<Self, Output=Self> being propagated to Subtrait, but that's not what happens. I can kind of see the logic that adding a constraint with Self on the left can't magically add a constraint with i32 on the left, but it would be so convenient!

Can anyone offer insight into what I'm trying to do should or should not work?

Playground link here.