Corner flags - an urban myth?

Many people seem to believe that only Clubs who have won the FA Cup can use triangular corner flags.

Research reveals no official confirmation of this. Mind you it didn't reveal any official denial either but, I would have thought, that if such a rule did exist it would have been relatively easy to find.

The rule on corner flags makes no mention of the flag itself, just the flagpost which "must be no less than 1.5 metres high with a non-pointed top"

I wonder where this myth (if such it be) originated.