It is true that Rust does not have a complete formal specification for its type system which has been analyzed and proven to be sound.

You seem to be implying that because of this, Rust has no definition of its type system (other than whatever happens to be implemented in the current compiler). I would disagree.

As evidence, I would like to point out that not a single person argued that this flaw was not a bug, but was in fact the officially defined behavior. Clearly, the community has a shared understanding of what Rust's type system "ought" to do.