Compiling with `sfgml_native_bytes` directive results in a compile error

[SunWukongsCommand]

import haxe.io.Bytes;

class Main {
	static function main() {
		var file:Bytes = sys.io.File.getBytes("test.txt");
		trace(file.sub(4, 5).toString());
	}
}

Trying to compile the code above results in a compile error if sfgml_native_bytes is set.
sfgml-dev\gml/std/haxe/io/Bytes.hx:259: characters 18-42 : gml.io.BufferType has no field BYTE_UNSIGNED
Without the directive, it works as expected.