Mismatched types on trait implementation with const generics

[Rexagon]

The following code gives a compilation error despite the fact that parameter A satisfies the required traits (Array, and A::Item: Copy).

smallvec = { version = "1.7", features = ["const_generics"] }

use smallvec::{Array, SmallVec};

trait StrangeWrite {
    fn expand(&mut self, bytes: &[u8]);
}

impl<const N: usize> StrangeWrite for SmallVec<[u8; N]>
where
    [u8; N]: Array,
    <[u8; N] as Array>::Item: Copy,
{
    fn expand(&mut self, bytes: &[u8]) {
        self.extend_from_slice(bytes);
    }
}

error[E0308]: mismatched types
   --> src/traits.rs:115:32
    |
115 |         self.extend_from_slice(bytes);
    |                                ^^^^^ expected associated type, found `u8`
    |
    = note: expected reference `&[<[u8; N] as smallvec::Array>::Item]`
               found reference `&[u8]`
    = help: consider constraining the associated type `<[u8; N] as smallvec::Array>::Item` to `u8` or calling a method that returns `<[u8; N] as smallvec::Array>::Item`
    = note: for more information, visit https://doc.rust-lang.org/book/ch19-03-advanced-traits.html

Am I doing something wrong or are there any problems with const generics?