coq.env.add-indt not preserving implicit arguments

[FissoreD]

The problem:
the API coq.env.add-indt does not preserve the implicitness of arguments while adding the new indt.

Code example:

Elpi Command add_indt.
Elpi Accumulate  lp:{{
  main [indt-decl X] :- 
    coq.env.add-indt X _. % simply adding the indt in elpi
}}.

Definition X (b : bool) := Type.

Elpi add_indt Record NoWheels {i : nat} := {
  (* the first and the third arguments of no_wheels are implicit! *)
  no_wheels (u : unit) {b : bool} : X b
}.

Expected results:
About no_wheels should say that Arguments no_wheels {i}%nat_scope n u {b}%bool_scope
however, we have, Arguments no_wheels i%nat_scope record u b%bool_scope

Test:
Check (no_wheels 0 _ tt true). should fail
Check (no_wheels _ tt). should succeed