I was surprised, too, when this occurred on my V3, last year. But I guess it's "by design", or as Isabeau said "normal".
Gen 1: Alpha
Gen 2: Beta
Gen 3: Gamma
Gamma died without having children. I pressed A+C and got a new egg, which hatched into Delta. Gamma appearred in the History list, but I could also see Beta and Alpha in the parent list, so it seems that Delta was Gamma's sister.