Is type inference working as expected here, or is this a bug?

# type record_type = { array_field : int array };;

type record_type = { array_field : int array; }

# let test_function_1 x = Array.set x.array_field 1 3;;

val test_function_1 : record_type -> unit = <fun>

# let test_function_2 x = x.array_field.[1] <- 3;;

Characters 24-46:

let test_function_2 x = x.array_field.[1] <- 3;;

^^^^^^^^^^^^^^^^^^^^^^

Warning 3: deprecated: String.set

Use Bytes.set instead.

Characters 24-37:

let test_function_2 x = x.array_field.[1] <- 3;;

^^^^^^^^^^^^^

Error: This expression has type int array

but an expression was expected of type bytes = string