It's not unusual. Girls won't like the following sentence, but this is what it is. Compliments are like giving your dog treats: if you give them out too much, she starts expecting them, but if you give them out sparingly, she'll adore it when you give her one.
Nothing's worse than giving a girl a compliment, and hearing, "I know," in response. It's like, "well if you know, then I don't need to tell you anymore."