"Wrong parameters" even with type-safe Eliom_parameter and Html5.F.a

[smondet]

While using the “normal” way of defining services, I got into a wrong argument parsing case.

Starting from a fresh project made with eliom-destillery, and the following modifications:

let main_service =
  Eliom_service.service ~path:[]
    ~get_params:Eliom_parameter.(
      sum 
        (set string "strings")
        (opt (int "left" ** int "right"))
    ) ()

and

let () =
  Test_app.register
    ~service:main_service
    (fun params () ->
      Lwt.return
        (Eliom_tools.F.html
           ~title:"test"
           ~css:[["css";"test.css"]]
           Html5.F.(body [
             h2 [pcdata "Welcome from Eliom's destillery!"];
             a main_service [pcdata "link1"] 
               (Eliom_parameter.Inj1 ["bouh"; "bah"]);
             pcdata ", ";
             a main_service [pcdata "link2"] 
               (Eliom_parameter.Inj2 None);
             pcdata ", ";
             a main_service [pcdata "link3"] 
               (Eliom_parameter.Inj2 (Some (42, 42)));
           ])))

On the generated page the link3 is broken (goes to “Wrong Parameters”).

I'm using Eliom 3.0.3 from Opam (and OCaml 4.01.0).