Associating %prec with a rule without any occurrences of tokens

[sgraf812]

I want to parse ML-style whitespace sensitive function application using operator precedence, so I'd start from a grammar like

%left APP
%%
e : "f" 
  | e e %prec APP

and I would hope that this would be accepted without conflict by parsing chains of whitespace-separated "f" tokens as left-associated lists.
Alas, it appears that %prec declarations only work if the rule starts with a terminal, or some other hidden condition:

$ bison -v test.y -Wcounterexamples
test.y: warning: 1 shift/reduce conflict [-Wconflicts-sr]
test.y: warning: shift/reduce conflict on token "f" [-Wcounterexamples]
  Example: e e • "f"
  Shift derivation
    e
    ↳ 2: e e
           ↳ 2: e e
                  ↳ 1: • "f"
  Reduce derivation
    e
    ↳ 2: e          e
         ↳ 2: e e • ↳ 1: "f"

If I use an arbitrary infix operator @ instead and specify %left @, all conflicts can be resolved.

Is there some technical reason why the operator-less use case can't be supported?