Pattern matching differences between ocaml and erlang

foo.erl

-module(foo).
-export([drop/2]).

drop([], Elem) -> [];
drop([Elem|T], Elem) -> drop(T, Elem);
drop([H|T], Elem) -> [H | drop(T, Elem)].

foo.ml

let rec drop l elem = 
  match l with 
  | [] -> []
  | hd :: tl when hd = elem -> drop tl elem
  | hd :: tl -> hd :: drop tl elem
;;