Okay, so about a month ago I was at the Power Plant looking for Zapdos and I kept running into lots of wild Pokemon. I then came across a shiny Magnemite, then I caught it. After that I ran into Zapdos and caught it. I headed to the Pokemon Center to go to my PC to see thier natures. The shiny Magnemite had an Impish nature and so did Zapdos. I was kind of disapointed Mangemite didn't have a nature that boosts Special Attack so I just left it there. Today I was training my Parasect so I can beat the Elite Four with it. I finished training it and I went to the Island 1 Pokemon Center to take Pikachu out so I can train it for the E4 too, then I just went to Magnemite's Summary page for no reason and it said it has a JOLLY nature. I know for a FACT it had an Impish nature when I caught it.
Is something wrong with my game? (I have LeafGreen.)