Coq does not use the notation for printing (with custom entries)

[amblafont]

Description of the problem

In the last line below, Coq does not use the notation "++" for printing (although it is able to parse).

Small Coq file to reproduce the bug

Declare Custom Entry mor.
Declare Custom Entry obj.
Notation "< x >" := (x) (x custom mor).
Notation "x" := x (in custom mor at level 0, x global).
Notation "x" := x (in custom obj at level 0, x global).

Parameter C : Type.
Parameters a b c : C.


Parameter op : C -> C ->  C.
Notation "x -- y" := (op x y)  (y custom obj, at level 40, left associativity).
(* displays "a -- b -- c" *)
Check (a -- b -- c).

Parameter op2 : C -> C ->  C.
Notation "x -- y" := (op2 x y)  (in custom mor at level 40, left associativity).
(* displays "< a -- b -- c >" *)
Check (< a -- b -- c > ).


Parameter op3 : C -> C ->  C.
Notation "x ++ y" := (op3 x y)  (y custom obj, in custom mor at level 40, left associativity).
(* displays "op3 < a ++ b >" (Coq 8.19.0 or 8.19.1) 
   instead of "< a ++ b ++ c >" (Coq 8.18.0) as expected *)
Check (< a ++ b ++ c >).

Version of Coq where this bug occurs

8.19.0,8.19.1

Last version of Coq where the bug did not occur

8.18.0

[herbelin]

Thanks for the report! This is fixed in #19089.