Unable to match bytestring (stream not consumed)

[agorer]

I am having some problems matching some bytes but maybe it is because I don't really understand how matching should work. As a reduced test case I have:

let%test "match bytestring" =
  let str = "\x01\x02" in
  let bstr = Bytestring.of_string str in
  match%b bstr with
  | {| b1::8, b2::8 |} ->
    print_endline ((string_of_int b1) ^ " - " ^ (string_of_int b2));
    true
  | {| _rest |} -> false

which as I understand should print "1 - 2", but instead is failing the test (getting to the _rest branch). If I change it to something like:

let%test "match bytestring" =
  let str = "\x01\x02" in
  let bstr = Bytestring.of_string str in
  match%b bstr with
  | {| b1::8, b2::8, rest |} ->
    print_endline ((string_of_int b1) ^ " - " ^ (string_of_int b2) ^ " - " ^ (string_of_int (Bytestring.length rest)));
    true
  | {| _rest |} -> false

I got "0 - 0 - 2" printed which means in this case it takes the first branch, but it is not consuming anything for b1 and b2 and rest is just the whole bytestring that was matched.

Is there something wrong in how I try to match bytestrings?