Eu posso encontrar pelo menos uma instância disso, de Relíquias da Morte . Depois que a varinha de Harry no núcleo de Phoenix foi (acidentalmente) quebrada, ele pega outra de Ron (que Ron havia roubado de um Snatcher). Ele parece ter algum problema com isso:
A large spider sat in the middle of a frosted web in the brambles. Harry took aim at it with the wand Ron had given him the previous night, which Hermione had since condescended to examine, and had decided was made of blackthorn.
"Engorgio."
The spider gave a little shiver, bouncing slightly in the web. Harry tried again. This time the spider grew slightly larger.
"Stop that," said Ron sharply, " I'm sorry I said Dumbledore was young, okay?"
Harry had forgotten Ron's hatred of spiders.
"Sorry. Reducio."
The spider did not shrink. Harry looked down at the blackthorn wand. Every minor spell he had cast with it so far that day had seemed less powerful than those he had produced with his phoenix wand. The new one felt intrusively unfamiliar, like having somebody else's hand sewn to the end of his arm.
Deathly Hallows Chapter 20: "Xenophilius Lovegood"
Há outros exemplos nos Capítulos 20 e 21, mas todos seguem o mesmo padrão: Harry tenta um feitiço bem simples com a varinha de abrunheiro, e isso falha bastante.
Obviamente, as regras para a fidelidade à varinha são complicadas (e nem sempre muito bem explicadas), mas Harry pelo menos parece acreditar que a "deslealdade" é a parte de seu problema, embora ele não saiba o que isso significa ainda. / p>