[Caml-list] Strange behavior of mutualy recursive definitions

[rixed@happyleptic.org]

I met this strangeness today and would like to know is it a FAQ? Is it
intentional? Is it fixable?

# let inc f x = (f x)+1 and dec f x = (f x)-1;;
val inc : ('a -> int) -> 'a -> int = <fun>
val dec : ('a -> int) -> 'a -> int = <fun>
# let rec toto = inc titi and titi = dec toto;;
Error: This kind of expression is not allowed as right-hand side of `let rec'

Now after reading http://caml.inria.fr/pub/docs/manual-ocaml/manual021.html#s:letrecvalues ,
this is unclear why toto and titi definitions are not 'statistically constructive':
It seams that one could trivially add a "fun f -> ... f" around the
function bodies in order to comply with the rules. And actually, this
even simpler (but to my knowledge equivalent) definition works :

# let rec toto x = inc titi x and titi x = dec toto x;;
val toto : 'a -> int = <fun>
val titi : 'a -> int = <fun>

So why was the first version rejected?