HashSet will accept duplicate HashSets

[RyanMarcus]

This behavior was quite surprising to me:

use im::{hashset};

fn main() {
    let hs1 = hashset![1, 2, 3];
    let hs2 = hashset![3, 2, 1];
    println!("{}", hs1 == hs2);

    let hshs = hashset![hs1, hs2];
    println!("{:?}", hshs.len());
}

Output:

true
2

I had expected the length of hshs to be one, since hs1 is equal to hs2.

I am not sure if this is an error in HashSet's Hash implementation (e.g., hs1 == hs2 but h(hs1) != h(hs2)) or me misunderstanding the semantics of HashSet.